Not sure if anyone has said this yet but most things inside the destiny universe re-spawns after some time. Let's not forget that even if goku is extremely strong, he still died a number of times. Goku also doesn't have a ghost to use to resurrect, he would need someone to wish him back to life which could also be a tedious task in collecting all the dragon balls. It'll be something to watch, yes, but by the looks of it; we'd end up expending his potential due to our numbers. Edit: the title just says "Goku" not a Version of him so... (Like if you agree)