If he runs, he will win. Even against Sandoval, who won't run.
How can you say that for sure? Barring Sandoval screwing up the first half of his second term, I think he'd do well against Reid in 2016.
Sandoval is not likely to run. Jon Ralston, the guru of NV politics, is fairly convinced that Sandoval is more interested in a federal judgeship than a senate run. I am inclined to believe Ralston given his track record. Anyway, even if Sandoval does run, I would think the race would be a tossup at worst for Reid. Reid has all the connections needed in Nevada and has a tacit detente pact with Adelson. I would expect the race to come down to turnout and the Reid machine usually prevails.