If Nats can't keep Rendon, they have to try to keep Howie Kendrick. He can still rake. He is good Ryan Zimmerman insurance, who will definitely be back at a reduced but not low salary.
If Howie or Rendon goes, keep Asdrubal Cabrera. Don't think you bring him back if both Rendon and Howie Kendrick are back.
No idea what the market is on Daniel Hudson. I do know the Nationals will never invest heavy into the bullpen over the offseason when almost every season it feels like they bring in good options around the trade deadline.
Matt Adams will either be back or be replaced by another lefty first baseman who can run into one and also sub in LF.
If Nationals lose Rendon, I'm not sure what they do in the lineup. Barring a move, Juan Soto's lineup protection is Howie Kendrick or Asdrubal Cabrera.