The basic premise of this whole thread is that the Democratic Party is being fractionalized by people starting a new party. The underlying assumption is that Democrats that have historically been active within the Democratic party are splintering off to start a new party, thus weakening the existing party.
However, I would suggest that this assumption is erroneous, given that the Bernie Sanders supporters (including those who registered Democrat during the last election) who are likely to be disgruntled with the Democratic party are unlikely to be historic Democrats, and more likely to have been unregistered, independent, Socialist, or Green. I doubt the creation of yet another additional party weakens the Democratic party at all, certainly no more than the formation of the Working Families Party did (which was statistically not at all), and it certainly doesn't look anything like "implosion". New parties are being created (and disbanded) all the time as part of normal political evolution.
You may take my criticisms of your premise as pedantic sniping if you wish, but it is simple disagreement with the entire fundamental premise of your post.