"Alt-Left" isn't a term. The only reason "Alt-Right" is a term is because that's what the right wing groups that hated the GOP establishment started calling themselves.
For the left it's usually just "progressives"
Mmm, no. "Alt-left" was an established term before Trump came along, used to refer to the subsets of the left that peddled "anti-war rhetoric" that was literally just war crimes denial and support for dictators, coined by those on the left who DIDN'T ascribe to such conspiracy theories. The right tried to co-opt the term to hit the entirety of the left over the head with, but that doesn't mean that there isn't an actually existing "alt-left".
As for what these people will do? They'll continue to peddle racist conspiracy theories about brown people protesting for democracy being a CIA psyop, like they have for decades already. Unfortunately, these people aren't going away.