Nic has been pretty reliable in the interviews he's given, other than giving the impression that Apocalypse in 9/8 would be played on this tour. And he's given a couple of interviews recently referring to his dad retiring after this tour is over.
I believe that is Phil's intention, to retire with the audience wanting more. His unlikely comeback as a solo artist and with Genesis didn't see him at his very best, but he gave his all and left us still wanting to see him again. Bravo, that is the way to go out. The only caveat, and I do see it as a caveat rather than a hope, is that Phil seems to come alive and be at his happiest when he's singing on stage. In time he may miss that and decide to do some more concerts, even if it's not a full on tour. And it will all depend on his health.
Ultimately for them all, the world is their stage. It's up to them individually and collectively. Mike & The Mechanics were active until right before this Genesis tour and could pick up where they left off. Tony doesn't have any live side projects and has always maintained that he doesn't see himself as a performer....but honestly if he chose he could put something together, guest with any Genesis related band or tribute band he chose, write songs with Steve Hackett (anyone else noticed Tony's mentioned missing that in recent interviews), or just put on his slippers and play Hogweed in his living room. Ultimately, though he may not see it this way, he's Tony Freakin' Banks and can do whatever he wants. I'm sure Daryl will find receptive musicians, he's well versed in many styles of music and very versatile. Nic's stock must be sky high and he'll be in demand.
RUmour has it that Gabriel is working on his I/O project again so we may yet see him take the stage again. Steve is being Steve, touring successfully, releasing albums that chart quite well. Ant is being Ant...making bread and butter from library music and himself available for Genesis related interviews...and his body of work speaks for itself.
As for a guest appearance by Gabriel or any other alumnus....I think that Phil singing Genesis out with Carpet Crawlers was just perfect. If Gabriel had come on stage last night it might have been better for him to sing something else earlier in the set. Or at an earlier gig. Ditto Steve or anyone else had they appeared. This was the line-up of Genesis that existed for more time than any other. Not my favourite but the best known, most successful, longest lasting...those three are close friends who have shared 50+ years of Genesis together. While it's clear that everyone still seems to get on with Pete, RIchard Macphail and probably Steve, this was a celebration of the trio plus Daryl.
Maybe it would have been appropriate for Peter and RIchard (who were in attendance) to take a a bow with everyone? Maybe Peter just didn't want to. In the end, we must understand that these guys did the tour *they* wanted to do...played and sang the songs they wanted to play...they did it their way. And it was a tremendous success. So long, and thanks for all the fish. If there are more fish from any of the (ex) members in the future, I'll consume them. But if not....they leave a fantastic body of work.