The problem with starting a 3rd party is actually getting enough support. Dems and Repubs are so entrenched as the 2 primary parties that it would take a miracle to get enough voters to follow a 3rd party. That, and I can almost guarantee both Dems and Repubs would absolutely go full bipartisan on making sure 3rd parties don't get any real power so the status quo of the 2 parties fighting to the death can continue.
I would definitely vote for Bernie, but it would feel like Sisyphus pushing the boulder: an uphill battle with no end.