Given the leviathan dlc in mass effect 3 what's to stop the leviathans from simply retaking the galaxy slowly, making everyone thralls if you destroy the reapers?
In reality nothing. But after countless cycles in isolation they probably would want to still keep to themselves obeserving the galaxy and only interfere if they themselves are threatened. Plus they tried to enthrall the galaxy once which eventually lead to the reapers creation so I don’t think they wouldn’t want to have a repeat of that
They don't have the numbers to threaten the galaxy. The reapers nearly wiped them all out. So their are hiding a few planets. Most likely trying to birth more Leviathans. So that one day they can subjugate the galaxy.