There are ways he can win the fight. Crazy stuff happens in MMA, people make mistakes, slip on the canvas, get cocky.
McGregor isn't one of those fighters who stays on the outside and avoids getting tagged at all costs. He takes risks and gets tagged occassionally. Dustin got him a couple of times coming in, so did Diego. Siver comes out swinging hard in rnd1 and if he tags McGregor coming in it's not unthinkable for a crazy KO to happen.
I don't expect him to win but it would be foolish to think he has absolutely no chance.
How you bet is up to you. +775 is nuts, I would throw a few bucks on it.