The most successful side the European professional club game has known – judged on their run of three wins and a narrow semi-final defeat in four incredible seasons – may have reached a critical juncture in their cycle.
It happens in every sport.
Should Leinster's elimination be confirmed at the culmination of this weekend's fascinating round 6 fixtures on Sunday evening – despite all their best efforts in Exeter – their supporters have every right to fear for the future.
It may well be a bracing time and a challenging one, too. Like all regenerations, there would be the exciting possibility of even greater glories to come – but it might also be prone to many pitfalls.
Jonny Sexton's contract negotiations, now confirmed as the perennial bluffing game by his main suitors Racing Metro, are still distracting, for all the bonhomie generated at Leinster training this week.
Sexton has been greeted with regular cries of "bonjour" and the like, but the well-publicised fact that he has spoken at length to his French suitors about his future – not his provincial or national coach nor, indeed, his team-mates – hints that the decision posts a vivid quandary in the player's mind.
Should Sexton decide to leave, particularly now that the IRFU are likely to pull the rug from under him as quickly as the French have tipped a jug of iced water on his head, will others follow?
And the imminent retirement of Brian O'Driscoll – who has yet to agree professional terms beyond next summer – may have been fast-forwarded after Declan Kidney's decision to strip him of the captaincy.
Add to that the fact that Joe Schmidt is unlikely to stick around after his natural cycle as coach is concluded in the summer of 2014 and there is a pile of uncertainty coming down the tracks.
That Leinster are much better placed to deal with it now than at any previous time in their history is, at least, some consolation.
Captain Leo Cullen, who has yet to confirm whether or not he will play on for another season – presuming he is asked, having only been offered a one-year extension last time round – understands attempts to paint a dramatic sense of an era perhaps coming to a conclusion.
"Two years ago, there was a similar situation with guys out of contract and there was a lot of talk about who was going to go," he smiles. "It is that time of year," said Cullen.
It's clear, though, that Sexton's removal from the squad would puncture a large hole, given the manner in which his rise in status has chronologically matched that of his club.
"It's his drive, that's the big thing," says Cullen, skirting poignancy in his tribute.
"He'll do everything to the nth degree. That's the thing that separates him from everyone else. You can see it in his body language during games.
"He demands success from everyone else. He has no problem bawling someone out. It happens regularly enough in training and he has no problem doing it in a match as well. He wants to be the best that he can be. And he wants everyone else to be coming up to that level as well.
"Obviously, he'd be a massive loss for us, so, hopefully, next year he can be a Leinster player as well."
As for the captain's own future?
His indispensability in big games this season has reflected poorly on Leinster's other second- row options. Bad luck and injury have conspired against them, but the absence of a Hines or a Thorn has forced Cullen to admirably burden a hefty amount of responsibility.
"There is a French club in from Federale 2," he teases. "It's a very big offer, it'll be in the papers next week. I'm not really too sure. I'm enjoying myself at the moment I'll make a decision over the next couple of weeks.
"There are always natural breaks in the season after the group stages. If you are not involved in the national squad there is a week off. Leinster have a couple of weeks off, so there is a bit more time to have a clear picture."
Whether Leinster will be left with anything meaningful to contest may not just colour Cullen's future, but that of a host of his influential team-mates. The consequences of defeat are manifold tomorrow; such that coach Schmidt was especially eager to dampen any talk of bonus points.
Leinster need to win to ensure that they can at least qualify for the Amlin Challenge Cup, in which they could also reach a Dublin finale, glean five ranking points and have the opportunity to once more hoist grateful Connacht into the Heineken Cup.
Never, it would seem, has there been so much on the line.