Bennett's death would probably mean either Mia Love or Jon Huntsman or someone of the kind gets appointed to the Senate. I don't see a successful primary challenge to Huntsman considering how good his organization was there in 2004/2008.
Since Gov. Herbert succeeded Huntsman, I can easily see him being appointed to the seat. Huntsman would then keep the seat as long as he wanted, probably, since he's extremely popular in Utah.
Herbert was actually Huntsman's Lieutenant Governor.
Speaking of Western Senators because of this, I think Brian Sandoval, Joe Heck, or Cresent Hardy would primary challenge Angle.