Yeah, I know that the Vegas Stadium seems more vaporware than real right now, but I don't know how long MLB can afford to have a team play in a 14K capacity stadium. If Vegas falls through, somebody will have to step up, even if it's an existing venue. And there's no way Sac can build a full-size stadium in that time frame. Plus, public funding in Sac is rough, as we know.
I have a tough time seeing the A's stay permanently - if Vegas falls through I'm sure somebody with an existing stadium will snap them up.