Last year, the film director Todd Phillips offered the convicted rapist Mike Tyson a cameo in his summer comedy The Hangover. Everybody loved the idea, Tyson shone in his role, and the movie went on to be a breakout critical and commercial success, generating almost half a billion dollars at the box office.

This year, hoping to repeat the trick, Phillips offered the convicted drink-driver Mel Gibson a cameo in The Hangover Part II. But no one loved the idea; in fact, some members of the movie's cast were openly critical of it. Within days, its studio, Warner Brothers, caved in to public pressure and gave him the sack.

That's how bad things have got for Mel Gibson, a two-time Oscar winner and one of the most talented actors of his generation. After a scandalous few years, he is now America's most toxic celebrity: less employable, on current evidence, than a washed-up boxer who violently raped a beauty queen and once bit off an opponent's ear.

If recent history teaches us anything, though, it's that Hollywood adores a comeback. Just look at Robert Downey Jr, who went to prison, twice, for drug offences, and just five years ago was effectively a junkie. Now sober, his victory over addiction has helped make him one of the world's most valuable actors, at the helm of the $1bn Iron Man franchise. Forbes magazine reckons he earns $22m a year.

Alec Baldwin's career has meanwhile thrived in the face of some thoroughly obnoxious behaviour. In 2007, he was taped calling his 11-year-old daughter a "rude, thoughtless little pig", who had neither "brains" nor "decency as a human being". Two years later, after a grovelling public apology, he hosted the Oscars, to widespread acclaim.

Even network television, which shies from controversy, will celebrate a repentant sinner. Charlie Sheen still earns $2m per episode of Two and a Half Men, making him the best-paid man on TV, despite having recently copped a plea deal for spousal abuse. And a recent incident involving a naked porn star locked in a hotel bathroom.

Mel Gibson's PR problems run deeper than most others, of course. They began four years ago, when he jollified an arrest for drink-driving by asking if the police officer who had just handcuffed him might be Jewish. "F***ing Jews!" he declared, after getting an affirmative response. "Jews are responsible for all the wars in the world."

This summer, things took a turn for the worse when Gibson split from girlfriend Oksana Grigorieva, who is mother of his eighth child, Lucia. In court papers mysteriously leaked to the press, the ensuing custody battle promptly saw him accused of punching her in the face.

A more damaging development was still to come, however. In July, the website Radar Online obtained several tape-recorded phone conversations, in which Gibson delivered a barrage of insults, threats, and racial slurs towards Grigorieva, repeatedly calling her a "slut". At one point, he declared: "If you get raped by a pack of niggers, it's your fault."

The tapes prompted Gibson's agents, WME, to terminate their relationship with him, a development announced on the day the internet site published a lengthy recording in which the actor drunkenly referred to a Hispanic employee as "wetback", and appeared to suggest that he could have Grigorieva killed, saying: "I'll put you in a fucking rose garden!"

Gibson now finds himself in a hole. Evidence would appear to suggest he is (in no particular order) an alcoholic, a racist, an anti-Semite, and a wife beater who goes around telling women that, for example they "need a bat in the side of the head". On the professional front, he has starred in little of note for five years.

In addition to the Hangover debacle, a film supposed to mark Gibson's return to serious form also faces an uncertain future. Called The Beaver, and directed by Jodie Foster, it is by all accounts a brilliant and clever comedy in which he delivers a mercurial performance. But its studio, Summit, has cancelled a planned release this year, and declines to comment on its future.

So things look grim from the Malibu home where Mel Gibson has been holed up in between court dates for most of the summer. And yet history suggests that it would be unwise to completely write him off. Though Gibson may never return to the glory days of Lethal Weapon and Braveheart – at 54, he could be too old – time could nonetheless bookend his career with a happy ending.

“As bad as things look now for Gibson, his misdeeds will fade into the rich tapestry of misbehaviour woven by the pantheon of American celebrities,” was how The Hollywood Reporter recently put it. “Given the frequency with which celebrity scandal is reported, you cannot underestimate how numb the public is to all of this.”

There is, as it happens, a tried-and-tested formula by which Mel Gibson can be rehabilitated, provided he has the discipline (and patience) to follow it. You only have to watch his brilliant turn as Hamlet to realise that he is too talented a performer to simply disappear.

His immediate priority should be to come out of the forthcoming court battle in one piece. Gibson faces what could be a double whammy: a custody case over access to Lucia, and a potential prosecution for verbal threats during his leaked telephone calls, and the alleged assault of Grigorieva.

So far, the legal process has been bruising. Gibson has kept almost completely silent, making no public comment on the string of allegations coming his way over the past few months. His ex-girlfriend, meanwhile, has hired and fired a string of prominent media advisors and lawyers and given several outspoken interviews, appearing on the cover of People magazine a fortnight ago.

In PR terms, that has hurt Gibson’s stock. But when the case eventually hits court, it could work to his advantage: he will be seen as measured, discreet and disciplined, while Grigorieva (who may yet be prosecuted for her alleged role in leaking the tapes) could look the opposite. “The judge wants legal cases litigated in the courtroom, where it should be litigated,” read a recent analysis of the case on The Daily Beast website. “After a certain point, if your PR campaign is too obviously playing out in the media, it can hurt you in the courtroom.”

Once Gibson’s legal woes are settled, he can stick his head back above the parapet and begin repairing his image. The first step on that front, according to PR protocol, is time-honoured: the public apology. It must be long, unequivocal, and preferably delivered in person, as well as writing.

Christian Bale would be a good act to follow: after he was taped delivering an abusive rant towards an employee on the set of the recent Terminator film, Bale appeared in person on a Los Angeles radio show, soberly declaring: “I was way out of order. I acted like a punk. I regret that ... It is inexcusable. And I hope that that is absolutely clear.”

Gibson must then embark on the second stage of rehabilitation: the actual rehab. This fulfils two roles. Firstly, it allows him to blame his most obnoxious behaviour on his apparent alcohol addiction. Secondly, it allows him to create a new narrative that revolves around cleaning his act up.

“The issue here isn’t that Mel Gibson hates Jews, or women,” says the Hollywood publicist Michael Sands. “He said what he said, but that doesn’t make it true. The issue is that he’s an alcoholic and a belligerent, arrogant drunk who has screwed up for too many years by not getting treatment.

“He needs to go to Betty Ford [rehabilitation clinic] for 30 to 60 days, and after that lay low, do his AA. He can then come out and say, ‘I’m sorry I have hurt a lot of people. I’m a drunk. That’s my story.’ Hollywood forgives. It will embrace you if you admit to having a disease.”

Finally, after a suitable period of quiet reflection, Gibson can begin performing once more. Here, experts are more or less united in the view that his first foray back into acting should be light and self-deprecating.

A guest appearance on Saturday Night Live, the weekly satirical TV show, would be perfect. A short internet film might also suffice.

“He can do a 60 second video on YouTube, all by himself, and say, ‘Hi, Mel Gibson here. I know you’ve been seeing a lot of me on TMZ and I want to say sorry for being an idiot,’” says the author and entertainer Gayl Murphy, who has interviewed Gibson on several occasions. “Or he could do SNL, or a clip on Funny or Die, like Paris Hilton did. What’s better than crazy playing crazy?”

Gibson’s long-suffering publicist, Alan Nierob, would no doubt agree. On Friday, he was placed in a comically tricky position when Liam Neeson, who also happens to be a client, was offered the newly-vacant cameo in The Hangover Part II. Through gritted teeth, Nierob told reporters Leeson would take the role “pending clearance of cast and crew background check”.

It was a reminder that, however ugly your predicament, laughter is often the best medicine.

Down Under, but not out: Mel Gibson's six-point recovery plan

Make Braveheart II

You can take our lives, but you can never take our careeeeeer! Gibbo could do worse than head back to Co Meath to resurrect his glory years as a blue-tongued, back-combed warrior with more enthusiasm for fist pumping than the cast of Jersey Shore.

Entertain the troops in Afghanistan

Robin Williams, Kid Rock, Jessica Simpson, JLo – they've all boosted military morale by putting on a show for the boys. Gibson, who has so often played the hard man on the big screen, could even help dismantle an IED if he wanted to make himself useful.

UN ambassador

If it worked for Geri Halliwell post-Spice Girls and helped transform Angelina Jolie from an alleged home-wrecking sex beast into a serious mother of six, becoming a rep for the UN could turn Gibson from anathema to humanitarian – provided he keeps out of the Middle East peace process.

Fund own epic

Having had box office-busting success with The Passion of the Christ (2004) and Apocolypto (2006), Gibson could step back behind the camera to direct something that unites, rather than divides his audience. A remake of Pollyanna?

Get another cameo on The Simpsons

Prove to the world you have a cast-iron sense of humour by going for a cartoon makeover. Everyone who's anyone, including Tony Blair and Michael Jackson, has dropped into Springfield. True, Mel had screen time with Homer back in 1999 but it sounds like a good time to plan a return visit.

Hide

What with his toxic views on pretty much all of humanity, Gibson could do himself a favour and simply to take to the hills. Having proved he can exist outside of society in Mad Max, going somewhere remote should be a doddle – and a big relief to the rest of us.