I bet b. snedecker in US open when i was in vegas awhile back but he withdrew before event. Do I get bet back?

Depends on the initial criteria set by the Book you bet at. IME, the betting sheet with the odds on it for these types of bets have those rules listed at the bottom of the page (i.e. "No action if player doesn't participate").

Your best bet is to call them directly and ask. I doubt anyone here will be able to give you a definitive answer.

TL;DR: You'll probably get your money back.

Yea it was at the Wynn. Don't get it back

Just pretend he played and lost. There was a 99.965% chance of that happening anyway