Ditching the milky way galaxy sort of makes the whole point of saving it in the first place pointless.
There isn't a single ending where you save it.
Control - you potentially doom it to repetition except it's eventual rebellion against the Shepalist rather than the Starbrat; best case scenario, everyone had better love their "benevolent" cyber-god - you've essentially done a God Emperor of Dune on the Galaxy.
Destroy - if the Starbrat is correct, you've doomed all organic life to eventual extinction; after the extermination of the Geth and EDI peaceful co-existence between any future AI and organics is unlikely... you've probably made matters worse overall, or you've had your Butlerian Jihad and there can never be another thinking machine I guess (as long as everyone in the galaxy got the memo).
Synthesis - you've mutated all life into cyborgs, granted that might save it but not in the form it was originally.
Refuse - all advanced races are extinct and the cycle continues.
You cannot save the Milky Way - it's screwed no matter what you do.