Sanders backs single payer, period. He did his whole campaign. He is supporting Obamacare only to the extent of the Reps not being allowed to revoke it, because it's all we've got. He backed Clinton because she wasn't Trump and no other reason. He's not a Dem. He's a the only savvy powerful progressive in the country, and he is not a Dem, he is his own man.
There is nobody else anywhere close to having the political clout, the organization and the platform than Sanders. Sure, grab yourself some total outsider who'd take a sword to the corporate fiefdom. He won't get on the ballot, now or even after the next collapse. Why, because of the ignorance of the US electorate is massively pervasive. Bernie is a truth to power politician, not a Quisling, as you are wont label. You got nobody.