Yup, you realize amazing things when you just lie on your bed for awhile and really THINK about the chain of events. It's amazing how easily everything can fall to pieces by removing just one player, even one that doesn't seem hugely significant at first glance. However, there is one key thing to keep in mind with this hell!universe: it only happens if no one fills the void Yamcha leaves. There's so many potential AUs here - meeting Tien early, so he becomes a much more central player rather than the sort of group outsider. Chaotzu has to step up his game because they need another heavy hitter, and thus doesn't fade into obscurity relatively soon after the start of DBZ. Bulma goes 'to hell with this shit' and builds herself a goddamn battle mech.
And then, of course, there's the AU I actually /went/ with. Which I'm not going to reveal here, because I'm actually writing it - don't know when it will be posted, could be this month, could be October, depends on how fast I write it out and type it up (because of course I have to write everything out by hand and THEN get it into a format I can actually post it in), but rest assured, the fic is coming.
And, just so you know? I like fluff. And shmoop. And I /don't/ like unhappy endings. So please have patience with me, OP, 'cause this ship is too cute to not happen!