Those guys have never fired a bullet on Assad (I fail to see any scenario in the future where Assyrians would). If im not mistaken theyre all around raqqa and had clashed with ISIS.
This is the US trying to find some kind of foothold against the Russian rise in Syria. Its not a bad thing, actually.
Not even Assad himself is under the delusion that the regime will come back in the same way it was, nor should it. What the Russian involvement ensures is that Assad or whoever they chose will be present on the settlement table and a part of the solution, and not its victim. Hopefully the major and leading part still.
What they need is some kind of opposition counterpart that they can involve and make a settlement with. I think the Russians will try to involve Egypt into a more active role with Syrian sunnis, and get it to "supply" a sunni partner for Assad and negotiate a settlement. But it will be a difficult task for Russia and its more likely that the Americans/gulf countries retain the sunni card.