Personally, I don't think the Nats window is at all dependent on Harper. But that's neither here nor there.
--- To say it again, I don't think Seattle sacrifices much of anything by going into this season trying to win. The same trades will be there at the deadline or next offseason. I think they can stay on the positive side and in my opinion that's probably better than being awful for an extended period. There is always time to be awful and maybe you can avoid it.
It's not all dependent on Harper. But he's leaving and their other players are getting older. They should be a good team but they aren't the powerhouse they have been. Their window is closing.
And the same trades may be available later but the value they get won't be.