Tonight Gay Byrne will present The Late Late Show for the last time. Naturally it will be an emotional occasion, as RTE's most successful programme, which practically spans the lifetime of the TV channel, finally becomes the late Late Late Show.

Or will it? As a brand name the show clearly retains obvious, if gnawing, attractions for RTE. But without Byrne, it could not possibly be the same.

RTE should do the decent thing and retire it with its presenter. In history, media, sport, politics, the arts, there is too often a ludicrous emphasis on Great Men (or Women). There are always other forces at work which contrive to allow a particular individual to reach pre-eminence.

So it is not because Gay Byrne is irreplaceable - though he is close to it - that the show must not go on. Rather, it is because the combination of Byrne and the programme is irreplaceable. Yes, Gay Byrne has been the most talented Irish broadcaster - but there is much more to it than that.

He came to the screen at a time when television was novel and when there were just three channels (two British - BBC and ITV, and one Irish - Telefis Eireann) available to Irish viewers. Indeed, most parts of the Republic then could receive only the new, Irish channel.

He also came to the screen at the outset of what has since come to be known as Ireland's Moral Civil War. Gaybo always had the timing of a real showman.

Forget the arguments about whether or not he was a liberalising influence or just a facilitator for liberalising influences. He was primarily the latter and, as his motivation was principally bums on seats, he understood the value of conflict. No conflict, no drama. Indeed, it should be remembered that the setting-up of Telefis Eireann and the by-now legendary Late Lates of the earlier years were preceded by bitter feuding about the likely effects of television.

Enter television. Enter, inevitably, the outside world. Enter, coincidentally, Gay Byrne.

The rest of the story - the unlikely mix of light entertainment and heavy issues, the priggish and pathetic wrath of certain bishops, the permanent possibility of sensation - is not only well known but has been discussed to death. "Something for everybody in the audience" very aptly replaced "Roll it there, Colette" as the show's most parodied cliche in its later, sponsorship-rich years.

What matters now is RTE A.G. (After Gaybo). As a showman himself, Gay Byrne would always be aware that the next gig is where the energy must be directed.

Much will be made by RTE's bigwigs of the wonderful contribution of The Late Late Show to public service broadcasting, and they have a point. But the case will be self-servingly overstated as the show, being in reality more showbiz than current affairs, also made wonderful contributions to certain favoured individual careers, not least its presenter's.

Even that is, by and large, fair enough. For the people running the station the focus will be, as it was for Gay Byrne, a matter of bums on seats. But the first phase (the sexual one) of the Moral Civil War has all but been resolved and the next one (the money one) is a legal minefield in which, by definition, wealthy people - people with clout - will wield their cheque books with even greater back-up than the bishops did their croziers.

Getting the low-down on stories comparable to the Charlie Haughey sex `n' money saga will not be easy.

Again, with perfect timing, Byrne has made himself a practically impossible act to follow. Who could blame him? Having gossip queen Terry Keane spill the beans on the second most famous man in Ireland (Gay Byrne is first) was a fair scoop for his penultimate show. How do you follow that?

It's not as if The Late Late Show had similarly spicy material every week - but it will be remembered (barring a gigantic catastrophe tonight) for ending on a high.

Various names have been mentioned as possible replacements for Gay Byrne as presenter of the show. But it has always - 37 years of it - been his gig. There may be young broadcasters with comparable ability to Gay Byrne. But if there are, where are they and why not give them a show of their own rather than ask them to work under the burden of a brand name that will never be theirs?

For RTE's head honchos, of course, it is about money, and that is partly understandable even if the conveniently high-minded stress on a public service motive is largely PR.

RTE A.G. will find itself in an increasingly competitive TV market and without its star player. Mind you, given the cost of its star player, it will have funds to enter the transfer market. But any replacement or revamped show will have lost the cachet which Byrne brought to the station.

Television, being fragmented now and novel no longer, will not produce stars like Gay Byrne in future.

There is a time for everything and the time to let The Late Late Show die is with the retirement of its presenter. It might be possible to keep it on a life-support machine, almost certainly at the expense of its first few presenters, until one came along who was noticeably more popular than his or her immediate predecessors.

The problem for any putative replacements is that they risk being seen as usurpers and they could very quickly find out that not all the Golden Age is imaginary. Ireland was a more distinctive State a few decades ago and RTE's best work was in allowing the State, up to a point (the story is still coming in . . . and how) to talk to itself. Gay Byrne's retirement genuinely marks the end of an era.

Good luck, Gaybo. But the ones who really need good luck now are the brass in RTE. Times have changed and while killing off The Late Late Show may feel to the brass like an agonising severance kiss, it is the decent and correct thing to do. Dignity, lads: that was then - this is now.

Eddie Holt is the TV critic of The Irish Times