Ultimately, Leo Cullen will end his long career with Leinster entirely of his own volition and on his terms. Not many head coaches can say that, not least after a dozen seasons at the helm, which is quite an achievement in itself.In seeing out his current two-year contract, this has also afforded Leinster and the IRFU a full year to find a replacement. Cullen will also be stepping aside at the same time as Jacques Nienaber, who is expected to return to the Springboks fold at the end of next season in time for the 2027 World Cup and South Africa’s bid for a third win in succession. Hence, Cullen’s successor will also have scope to bring in at least one key assistant.All in all, the timing feels right. It must be a hugely demanding job overseeing the province’s schools, academy, clubs and senior squad. Hence prop Jerry Cahir is plucked from the AIL in a crisis.There are also the restrictions imposed by his and Leinster’s IRFU paymasters, and the province have been the bulk suppliers to Ireland’s team for the duration of Cullen’s tenure, witness supplying 26 players to Ireland’s Six Nations squad and 18 in the initial squad for the forthcoming Nations Championship. As they also supplied a record 14 players to the Lions last summer, to reach the finals of both the Champions Cup and the URC this season was exceptional.Yet, Leinster are being required to increase their contributions towards their 11 central contracts from 30 to 40 per cent, and 11 is actually a paltry sum and contributed to the departure of James Lowe. Then there’s the extremely high expectations of supporters, sponsors and the media, with anything less than a Champions Cup and URC double regarded by some as a failure.Leinster's Leo Cullen celebrates after winning the Heineken Cup final against Northampton Saints at the Millennium Stadium in Cardiff on May 21st, 2011. Photograph: Glyn Kirk/AFP/Getty Images In his 11 seasons as head coach to date, Leinster added a fourth Champions Cup in 2018, when Cullen became the first man to both captain and coach teams to the title, as well as adding six more Pro 12/ Pro 14/URC crowns. There have been a whopping 13 finals in 11 seasons, yet the stick with which to beat Cullen is that Leinster have lost their last five Champions Cup deciders.It is some juggling act to remain competitive on both fronts and there’s no doubt Cullen has made some mistakes, albeit Leinster also had little luck in some of those deciders. They also remain the only URC team to reach a Champions Cup final since they beat Ulster in 2012. It’s also worth remembering Cullen was promoted, perhaps a tad too soon, to replace Matt O’Connor after Leinster had finished fifth in the Pro 12 and missed out on the playoffs. Cullen’s difficult first season saw Leinster lose five of six European pool games and lose the Pro 12 final to Connacht, but since bringing in Stuart Lancaster and subsequently Nienaber, Leinster have now won their last six Pro12/URC finals.Retaining that title last Friday night at Croke Park with their 36-7 win over the Bulls had no bearing on Cullen’s decision. He had already informed Leinster and the IRFU of his desire to step down after one more year. In fact, regardless of that result, Cullen could have stayed on longer had he so desired.Clearly, though, the demands of the job have taken a toll. That was evident in his broadside at the media – “You guys love putting the boot into us when things don’t go well” – after the Toulon semi-final win. Maybe this also reflected the departure last December of his long-time press officer Marcus Ó Buachalla, whose full-time successor has only recently been decided.Although Leinster reached the Champions Cup final, there’s no doubt they had a favourable home route to Bilbao against teams who finished in the lower regions of their domestic leagues. Whereupon, they were effectively beaten by half-time in their poorest performance in a final. But that also added to the nagging suspicion that winning the Champions Cup is becoming increasingly hard for Leinster in an era of unprecedented French dominance.Despite those concerns, and the role’s restrictions, the job should appeal to many good coaches. There will inevitably be speculation linking Lancaster with a return to the province after his success-laden six years as Cullen’s right-hand man, all the more so as his two-year contract with Connacht also expires at the end of next season.Another intriguing possibility would be Ronan O’Gara, given his contrasting history with Leinster as a playing and coaching foe with Munster and La Rochelle. As it happens, his current contract with the Top 14 club, which he has guided to two Champions Cup final wins over Leinster, also expires at the end of next season. Were it to come to pass, it would certainly be a courageous call by O’Gara and Leinster/IRFU.Why is Leo Cullen leaving Leinster? Listen | 17:22Noel McNamara is another with a working knowledge of Leinster’s pathway who has been generating quite a CV with first the Sharks and latterly Bordeaux Bègles.With Andy Farrell having penned another four-year deal to extend his stint into a third World Cup cycle, the job of Ireland head coach is closed off for another while yet. But if Cullen’s successor has a successful stint with Leinster, he would be the heir apparent.An additional slew of high-profile coaches will become available after the 2027 World Cup, including Argentina boss and former Leinster playing star and backs coach, Felipe Contepomi. Were the union and Leinster to go down that route and target a coach stepping down after the World Cup, it could yet be that Cullen might be persuaded to stay on for a few months to ensure a smooth changeover.After all, Cullen has always done whatever he’s felt is right by Leinster.gerry.thornley@irishtimes.com