If Sanders somehow wins the primary

Absolutely, I would vote for the winner of the Democratic primary. Because above all else I don't want to let the Republicans drive us right into the ground to benefit a few rich guys.

I just don't want to see another fiasco like 2016.

I suspect even the most neo of Democrats would vote for him as well, just to prevent Republican mischief. Remember, even a full blown Socialist President would have to enforce laws passed by a pretty centrist mixed-bag of Democrats in Congress. Socialist Paradise is not going to happen by one Socialist in the White House.