The first campaign I ran, crikey, the end was a high point. Our Chopper pulled a "get a gang" move from another play book and calmly declared: "Those things in the tunnels, that have been picking us off one by one? I want them as my gang."
So then the whole story came out about the gap between this world and the world the aliens had come from. About how the leaders of the world-that-was managed to close the rift back during the Apocalypse, and about how the creatures that were stuck on this side were slowly trying to open it again.
The savvyhead had salvaged a nuke from a stealth bomber that popped out of the air one session, having jumped fifty years forward in time from the run it had been on. The hocus had been preaching all game about how heaven was the transcendence of the flesh, and about how we were destined to step beyond. It seemed logical when the one took his bomb and the other took his followers and they both stepped into the newly opened rift between worlds and blew up whatever they found.
I think the final scene was the driver, bus full of the NPCs that made it out alive, heading out into the wasteland into who knows where.
Yeah, I could see that the big issues in the background were going to flop out all over the table, and that when they did something was going to have to be done about it. I don't know how obvious that was to the players though. It was a good session, there was a lot of "Oh, that's what the deal with XYZ was. That makes sense!" which I always love as a GM and which seemed to happen with very little forethought on my part. It tied things up neatly. But then, there were also social pressures on us to end the game, so we were all psyched to push things hard.
The second one, well, the characters had gone in very different directions geographically, and the players were bored of not interacting, so we called it to a close. Wrapped up things that were outstanding, but it was functional, not a climax.
This is a really interesting topic and I hope we get more answers out of it!