I wouldn't assume that switching parties will save the seat for him. We aren't talking about a seat in Oklahoma or Kentucky here. He'll lose a lot of the Democratic votes he gets here and will have to rely on gaining Republican leaning ones to get him through. Not impossible, but it's not that easy either.
Well, it's not OK/KY, but it swung right about as hard as Ohio did in 2016 and Republicans picked up a bunch of overlapping and nearby state legislative seats this year. I think this areas is pretty gone for Dems going forward.
No, at least not necessarily. There's a lot of moderates in the districts who voted for Democrats out of New Deal era ties, but it still voted for Obama twice and has Atlantic County in the district. The education attainment divide means that trends are going against the Democrats by this isn't a goner by any stretch of the imagination. A stronger candidate than Van Drew (an actually pro-choice, pro-SSM candidate with ties with Atlantic County) would be doing alright here.