1. The Beatles -these are the guys to beat in the never reformed stakes. If Lennon hadn't died? It had been a decade since the band had gone swimming with the fishes and they hadn't yet but might they have? Maybe, very lowkey would be my bet, or maybe some big charity gig. Maybe the nuclear disaster in Japan would have done it. but Lennon was murdered and it never happened.
2. The Band – Yeah, Robbie Robertson didn't merely burn that bridge, he blew it up, repaved it and blew it up again. Leon Helms was furious at Robbie for hogging all the glory and loudly decried it. Robbie shrugged and said he was only telling the truth. So even if Richard hadn't ended it all, it wasn't going to happen.
3. The Clash – They would have reformed and recorded new music. I bet the rent. Indeed, did you read the post I wrote about (well cut and pasted about) Joe's daughters, they thought a reunion was inevitable as well. The closest e got was that Acton gig all over the new (old) album.