I'm sorry man but it's clear you have absolutely no idea what you're talking about when it comes to this stuff.
A player can't simply go back on a LOI for no reason. That's the point of a LOI.
Unless UCLA voids his LOI (or he fails to qualify by NCAA standards) he can't play college baseball anywhere else.
Now, if he's only a verbal then he can do as he pleases.
That's what I'm talking about. He can go back on his LOI and not play college baseball for a year.
Doesn't mean he can't sign with the Nationals. Doesn't mean he can't go to school somewhere else. He just has to wait out a year.