Assuming no FA signings and everyone is healthy, I see this:
C - Ruiz, Adams
IF - Smith, Garcia, Abrams, Kieboom, Menesses, Alu, Vargas
OF - Thomas, Robles, Garrett, Rutherford
Call is stashed at AAA. Crews, Woods and the like won't be considered until May. On the infield, I can see not bringing back Smith and/or Vargas and going all youth, but you need a few vets. The Nats have been really lucky on the injury front this year. Zero starts missed by the rotation, both catchers are healthy, and minimal disruption to the infield or outfield besides Robles. His being gone hasn't really been disruptive. That isn't going to last to next season, or next week maybe, so let AAA get stacked with with guys who will either crush their way to a promotion or will step in when someone on the 26-man gets hurt.