I'd argue for retagging and removing it - since the tag on its own is a meta tag. There's no real value for it on its own.
I've retagged the questions, though looking through them, migration wasn't always the right tag. I've gone with migration-path-request in some cases, and completely different tags on another.
Some of the questions were confusing, referring to a primodial meta.stackexchange that predated the Meta.Stackoverflow that became Meta.Stackexchange (and not the Meta.Stackoverflow we have now), and didn't really have any historical value on their own so were deleted.