Sandoval has a 13 point lead in the primary. He should win it easily. I doubt the undecideds at this point will go back to Gibbons. They wouldn't be undecided if they hadn't been turned off by him. 75% of the NV GOP doesn't want Gibbons. I think I can rest a little easier about this race.
Generally, challengers can expect to win the bulk of incumbents (I suspect this is just as true of primaries as of general elections, though primaries are more difficult to poll). With that in mind, I would agree; Sandoval is in pretty good shape.