Keith Duggan/Sideline Cut: Although still a long shot, the thought of Roy Keane as the future manager of the Republic of Ireland is both attractive and plausible.

It was funny to watch Keane on the charity circuit in Ireland this week, playful and engaging and offering light-hearted equivocations on his recent intimation of his own mortality.

Keane's statement of intent to bow out after the 2006 season must have come as a jolt to the many people who, whether an admirer or not of the singular Cork man, have come to think vaguely of him as an inextinguishable life force. For Alex Ferguson, the admission that Time's perpetual march would soon eclipse his greatest warrior must have sharpened his own awareness that the glory days are numbered and the days ahead are precious.

Keane's revelation that Ferguson subsequently marked his card on when and how he would leave the game was a fond acknowledgement by an old school professional of the fact that the Gaffer still calls the shots; but it meant nothing. If there is one thing certain about Keane, it is that he is both intelligent and scrupulous enough to get out of the game the minute the signs of irreparable deterioration visit upon him, as they do all the great athletes.

Ferguson has publicly agonised over his own days of pasture, announcing and retracting his intention to move upstairs and view affairs at Old Trafford from a leather armchair, but Keane's presence in the dressing-room must be a comfort to him. One by one, the faces who once seemed central to Ferguson's bid for greatness have shuffled off: Steve Bruce, Gary Pallister, Eric Cantona, Mark Hughes, Denis Irwin. Mature and greying men now.

The kids are all grown up. Paul Scholes' career is in its autumn. Lee Sharpe is a nostalgic memory. Ryan Giggs is now in his thirties, David Beckham a scarcely recognisable figure.

Through the tumult, Keane has remained constant and immovable, and, while he leads, Ferguson can convince himself the landscape remains unchanged. But if the Irishman goes, surely he would take with him some of intangible element of the fight that has kept the Scotsman hawkish and his sense of grievance sharpened? Surely when Keane leaves, Ferguson will at last feel old and tired.

It would be tempting for Ferguson to try to coax one last season out of Keane, to try to persuade him to fight the one fight that the Irishman would be certain to lose, that against ageing. Whether Keane makes his exit in the bathetic fashion which would pull at Irish heart strings - magnificent defeat, tears and tricolours and one last chorus in a German stadium - or if one day he simply does not turn up for training, does not matter. What is certain is, relatively soon, Roy Keane will not play football anymore.

That thought inevitably carries echoes of the scenes following the 2002 World Cup when the intelligentsia queued up on the Sunday morning talk shows to offer a diagnosis on Mr Keane. They said he was a dark, tormented soul. They said he would be haunted by what happened that summer when he began his afterlife as a footballer. They said he was symbolic of the hard and new Ireland where the win is the only thing.

It would all have been highly laughable stuff had it not been so presumptuous and deeply insulting. It was the stuff of Punch magazine, all but depicting Keane as a fringe lunatic destined to spend his days roaming the moors outside Manchester.

Flash forward to this week, and the calm and (relatively) sunny figure happily doing the interview thing for his chosen charity, the Guide Dogs for the Blind. He said this week what he said in the midst of that national meltdown in the summer of 2002: that everything which occurred was a football matter, a management matter. He carries no regrets because at the time he was clear about his position while, all around him, others grew more muddied and ambivalent in their reasoning.

Within the gossipy and essentially disloyal arena where old professionals turn a buck as pundits, many wrong calls were made about Keane also. He was declared wrong for leaving Ireland's camp, and it was widely predicted he would not come back. Both before and after his hip injury, he was deemed a paling force in English football.

But at the business end of this season, after he silenced the claims of Liverpool's Steven Gerrard as the supreme midfield operator and took ownership on a fraught evening at Highbury even before he led his team onto the field, much newsprint has been dedicated to Keane's abiding greatness.

So we have arrived at the point where Keane is contemplating his leaving of the game in a serene state of mind, already vaguely turning his mind on what he may do afterwards. Inevitably, the old chestnut of someday managing Ireland arose and Keane could not resist making a swipe at the FAI.

Still, Keane has never let the FAI be a stumbling block, swallowing the antipathy he holds towards the association so he could answer his heart's call to return and play for Ireland under Brian Kerr. If Ireland do qualify for the World Cup, circumstances could alter greatly. As the past has shown, the major summer tournaments hold a ferocious grip on the Irish psyche. Kerr, like Keane, is a meticulous dreamer, at once a hopeless football romantic and a tough, organised football coach. A successful tournament for Ireland and a last hurrah for Keane would see him depart the stage basking in general public affections.

In setting his reputation in stone at Manchester United, becoming one of the handful of immortals to play at Old Trafford, Keane has also become the trusted confidant of one of the key football men in post-war Britain, Alex Ferguson. From his early rejection slips to his late blossoming, his lonely hours in north of England jail cells, his drinking days, his on-field arguments, his injuries and his gradual evolution from shy Mayfield lad to the guarded and sophisticated club spokesman, Keane has experienced it all. The advice he can impart to younger players making their way in the game has to be worth something. His transition from the reckless, box-to-box marauder of yesteryear to the sharp and clinical holding midfielder he has become, the simple precision with which he plays the game and his survival at the top level for so long bodes well for his prospects as a manager.

Brian Kerr's tenure in Ireland has every sign of being a long and happy one, and such is his twinkling authority it would seem a good bet that he will finish the Irish job on his own terms.

But the day will come when the vacancy arises and with it the clamour for Keane to occupy the very position and place against whose previous occupants he so fiercely rebelled. It may seem far-fetched, but then Roy Keane's entire career has resonated with a sweet, contrary note that becomes more clear and appreciated with each passing season.