I don't know how willing they are to give up Crimea and I suppose one of the reasons the war is happening now is that the west closed their eyes when Russia annexed areas from Ukraine. At least on the news Crimea is often described as 'temporarily occupied', so I think at least offically they're targeting 1991 borders.

But yeah, it's solely up to Ukraine, and I believe they'll have very similar support regardless of the border, at least as long as they're not claiming anything beyond 1991 borders from Russia.