When Vriska made John fall asleep and forced Bec to become Becsprite (and then the power-up of Bec Noir) she made it clear that she intended to end the problem as well. From that point on, the Trollsteroid (I like that... I claim that) was doomed.
So everyone on it was dead anyway, Noir had no problem wiping it out. Hence, the entire sober!Gamzee murdering arc was pointless. Or, there's something going on that we don't know about. Like, where's Jadesprite? Where's Aradia? Was future Karkat (the memo FCG) spending his trolling time taunting himself in the past while typing in a room full of corpses?
I did some looking in the archive. I can't find the FCG pesterlogs from future Karkat's perspective, where it seems he's trying to contact future Jade, presumably about whatever The Plan is. As far as I can tell, Karkat just loses his shit and runs to the lab, contacts Equius re Gamzee, then the honking murderspree.
That seems to imply that we are, in fact, watching a doomed timeline, as corpse Dave from his dead coinflip outcome could talk to rap-off with dead Tavros.This would explain where Aradia has been (in the alternate dead future memory bubbles), and since we're in one of Doc's blind spots, he could have easily taken the dead timeline dreambook and extrapolated a non-alpha outcome. We're getting near his death, so his omniscience is running out.
Anyway, that's one theory. May not be true, but it fits a lot more facts than the two fallow universes and a meaningless resolution to months of plot.