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.
As far as I can tell Republicans only picked up Van Drew's old state senate seat and the assembly districts, not "a bunch of overlapping and nearby state legislative seats". Three seats is not "a bunch" and that particular area has been traditionally Republican for quite a while.