That's not really the nightmare scenario because Hillary would be president during the GOP supermajority. The real Dem nightmare looks something like this:
Current: 54R/46D
2016:
-Republican wins by 4-5%, carries every Bush/Obama state but NM, also carries WI and PA
-Dems pick up IL, GOP picks up NV and CO
After 2016: 55R/45D
2018:
-Republican president has ~50/50 approval
-Dems pick up NV, GOP picks up WV, IN, and MO
After 2018: 57R/43D
2020:
-Republican president wins reelection by 7-10%, carries every state Obama got <56% in
-GOP picks up VA, MN, NH, NM (with Martinez), Dems pick up ME when Collins retires
After 2020: 60R/40D and 6+ years of GOP-controlled federal government
Never going to happen.