I don't think so. The crazy left are the dynamic base of the party. Either they will nominate a Sanders clone in 2020 or the party pick will sound like crazy Bernie to try and get the base out. The result will look like 1972 for the Dems but I suspect it will just generate more of ‘where is our Watergate dreaming’. Until the Dems hit rock bottom they won't start trying to behave normally. The big problem is half the GOP at least are Uniparty squishes and can't be relied on to be anything but greedy cowards.
Great observation, the Democrats today have a “crazy left” base whereas years ago they had a union base, workers as much as anything else. The identity crisis is going to take a few years to work out as the older, more moderate Democrats eventually move on. Unlikely a viable third party will form so Republican’s will benefit. Should the Democrats get truly saddled with the “crazy left”, we’ll likely hear talk of a Republican majority for a generation. Live long enough and the cycle is bound to happen.