Rising star Byrne ready to challenge the perfect ten
While there will be plenty of gnashing of teeth and wringing of hands at the departure of yet another gilded young Irish talent, at least Leinster can confidently assert that they have some groundwork laid for the future.
Ian Madigan's understandable wish to spread his wings and fly is regrettable for many selfish reasons; in truth, there are fewer sports people one might wish to pay in and see play. The 26-year-old was capable of anything and hence persuaded punters to part with their hard-earned.
Not everything he did came off and Irish rugby's historic mistrust of the unpredictable - even Australian Matt O'Connor seemed to receive a transfusion from the Irish blood of some or other distant antecedents - mitigated against over-indulgence in his, admittedly, often wayward talents.
And yet his ledger offered a surfeit of debit; he easily surpassed the requisite percentages for a top-class goal-kicker and the abiding memory of his time at Leinster will be of a game-closer rather than a game-choker.
Sure, the many advocates of the devil will attest to his intercept pass in last season's Champions Cup semi-final against Toulon but he was guilty of trying something in a game when few others shared that same desire; his tears after the World Cup game in France were not of celebration but of affirmation.
When he does return to Leinster, as presumably he will at some stage, he will be an even better, more rounded player and personality; until then, Leinster posses a world-class Jonathan Sexton who will emerge from his current fug of harsh self-examination.
Madigan, orchestrating elsewhere rather than ensconced as a frustrating second fiddle, will need to be superseded by a competitive array of challengers to Sexton's pre-eminence; as important as the Irish out-half is to Leinster, the benefit of realistic competition to him is vital for the province's health.
Leinster have already provided a stern examination of the options available during the World Cup window which offered tentative shots of progress in a hugely encouraging Pro12 opening stanza minus their 20 internationals.
"The World Cup period was brilliant," agrees the sadly retired captain Kevin McLaughlin, "in that it allowed us to see some of these guys in high-pressure situations, and in tough games.
"There's the likes of Ross Molony, Cian Kelleher, Garry Ringrose - Cathal Marsh got some game time as well - who stepped up during that period and played some really good rugby. Guys to look out for in the years to come, and guys that I can say with a great deal of confidence are going to be at Leinster for a long time to come. So it's very exciting."
Of the aforementioned, Marsh is an out-half option but McLaughlin was also impressed with another name - that of Ross Byrne, whose exploits with the Ireland U-20 side, albeit a not always consistent bellwether of future fortunes, franked his status as an emerging star.
Given that Leinster are now officially out of European contention, Cullen has another chance to give his younger cadre of players more experience of first-team action but in a more hostile environment; Byrne may not necessarily start but he should be afforded the chance to play in their remaining two games.
Byrne admits he has already learned so much from "the best out-half in the world". Now he should get the opportunity to play alongside him.
"When you're watching him, you have to admire him," the ex-St Michael's College man said recently. "He's probably the best out-half in the world right now, I don't think there's much doubt about that."
It stands to reason, then, that Byrne's more meteoric rise might propel him ahead of his colleague and, as the rest of the season unfolds, the wider rugby public may get a glimpse of the many reasons why this is so.
The comparisons to Sexton are obvious; he is a supreme goal-kicker, can take the ball to the line at risk of physical punishment in a quest to find runners to break open holes in opposing defences and he is unerringly accurate with his touch-finders.
He is built impressively for the modern game, standing 6' 2" and weighing north of 90kg, so he is already well able to withstand the brutish nature of modern rugby.
But, as he showed with Nigel Carolan's wonderfully expressive U-20s in the Six Nations last spring, he thrives in a free-flowing game where punching holes and finding space, rather than ramming into brick walls at the expense of slow recycling, is the key to unlocking defences.