The window for the Nationals is going to get bolted shut when Harper bolts. They'll just end up like the Mets now. Pitching but no hitting.
Robles, Soto, Turner, Eaton (if he can stay healthy), Rendon and of course Matt Adams. Seriously, they have a core to build around. What they've been doing is what the Braves stated that they
wanted to do, reload instead of rebuild. Harper's making $22M this year, Dan Murphy $17.5M, Gio is making $12M, Wieters is stealing $10.5M, Madson $7.5M, Kelly $5.5M, Doolittle $4.35M plus $1M buyout.
Zimmerman gets a $4M per raise (done in 19 w/$2M buyout), Rendon will likely get a raise through arby, say $4M, Scherzer jumps from $15M to $35M per (plus he gets paid a bonus and I'm not sure how they account for that) but his 19, 20 and 21 salaries of $35M each year are all deferred without interest until 22-28 in $15M installments so it looks like he's only up for $15M in 2019 if his bonus is accounted for in that year when it is paid, Strasburg has a similar weird deal where $70M of his money is deferred for years 19-23 where his carrying number per year only looks like $15M for 2019. So short term, neither Scherzer nor Stras get any kind of raise.
So, best I can tell, They shed about $78M in guaranteed contracts and look to have less than $10M in raises they will have to account for.
Cots has them at $181 for 2018, the Braves at $119. So, if you take the $62M difference there already and add in the $78M they shed, then the Braves would need to clear (or combine with an increased payroll) $140M prior to offseason 18-19, just to have as much to spend as the Gnats will have this offseason. Yet the Gnats have 2 aces under long term control and most of a core to build around. While, overall, their farm isn't as strong as the Braves, it's not bad.
I don't see them going away any time soon. However, they may be in trouble when they start paying the deferred dollars for guys not pitching in the mid 2020's.