I think it will be good for Democrats but not for any of the reasons stated.
1) No Trump on the ballot = no low propensity Trump voters
2) Democrats hate Republican senators almost as much as Trump
3) College educated voters are basically now firmly part of the Democratic coalition and they turnout during midterms
4) Even with Republicans controlling redistricting, they have less control than they had in 2010 and population shifts mean rural areas will get less representation
5) Republicans have more exposure in the senate
Another issue is that a lot of rural areas now vote 80% Republican, as opposed to 60% Republican 10 years ago, so the GOP will now experience similar issues with vote-packing in rural areas that Dems experience with vote-packing in urban ones.
My thought as well but redistricting and gerrymandering may be especially tricky this cycle if Trump did indeed bring out voters that other wise would not have come out.
I also do not know if the Texas and Florida GOP will trust Hispanic Majority Trump districts which can be drawn now..