I am not convinced Warren would have won. Clinton got enough votes, but just not in the right places. One would have to argue that Warren would have fared better in WI PA OH MI than Clinton. Clinton did shoot herself in the foot with her coal comments, so maybe there is an argument there. But Warren is heavy on ideology and his version of facts, which seem to bore the electorate. As much as Clinton is hated by half, she is loved by the other half.
There’s that; plus the fact that Warren didn’t even get as far as Bernie Sanders in the primaries against Clinton.