They already completely ruined their chance at taking the tipping point state (NC) given the Libertarian, the Constitution guy, and Tillis' polarizing nature in the legislature.
No. Tillis may have been the best possible candidate, except for maybe someone like Sue Myrick. Of course, he's still not great, but the GOP still has about a 46% chance of winning.
No. Jones is too libertarian to get through a primary, and wouldn't be too strong in a general. Miller would not primary-challenge Hagan. Forest is a tea partier who, IIRC, is prone to gaffes.