They can't really "collapse." If they go 2-3 in this series and 1-2 against the Marlins that's basically the team we saw all year (or at least since June 1) so if they come up one game short that's hardly a dramatic difference. Of course they should win the Marlins series, but...
It'd be nice to take the DH tomorrow just to keep the Nats from clinching. We can also help force them to play in Milwaukee. And not finish in fourth place, which really would be pretty poor optics. OTOH, they could end up picking 15 instead of 17th.