Mars?
Mars indeed would be the only place left to go, at least as far as any organized society is concerned, should the super volcano blow it’s top.
This isn’t something anyone can “prep” for, with skies around the globe literally darkened for years by volcanic ash, no crops are going to grow anywhere, not to mention global temperatures plummeting us into a form of a natural nuclear winter. Again for years.
It’s an “ELE” (extinction level event), like was said in the movie Deep Impact.
So like death itself, this is pretty much not worth worrying about, because nothing can be done to avoid it or its impacts.