He will only take votes away from the Dem nominee and allow the GOP candidate to win.
Not necessarily. There's still groups of Republicans who like him and will vote for him. Not necessarily huge ones, but still. I have a few family members who are Republican who voted Crist last time and would/will next time.
Anyway, in a Crist/Sink/Scott match up I'd expect either Sink or Crist to collapse pretty quickly and consolidate around whoever looks stronger. But really, the likeliest thing is Crist running as a Democrat, probably beating Nan Rich and Alex Sink. Then again I think people underestimate Sink a bit too much, I wouldn't put it past her to pull it out.