I don't think the Dems are going anywhere unless the Reps decide to say "fuck it" and openly embrace dictatorship. It's just too valuable to the system as a whole to have two options, or at least the appearance of two options, for people to squabble over. With a single party that's a single point to lay all your grievances on and a single entity to blame.

Both parties have the same ultimate goal of catering to the bourgeoisie but it's incrediblely valuable to have the optics of wider support.