He's got a snowball's chance to make the Dem ticket, but if he does I'll back him the whole way. If Hillary and (Random Republican) are there in 2016, I'll just do a write in and call it a day.
Even if by some miracle Bernie becomes President, nothing will really change in the U.S. Those who are really in power have no incentive to actually reform anything, whether it be the tax code or govt spending priorities. Only a total economic collapse similar to the 1930's would shake things up sufficiently to enable reform.
But hey, single payer health care and a fair tax system is nice to dream about.