Even if those guys walk, there is likely enough talent around to compete for the next few years. It might be a matter of going from a true talent 95 win team to 85 wins but that is still within striking distance for the playoffs every year. Hell the Royals and Giants were probably something like true talent 85 win teams in 2014.

There are some good players in the minors and Rizzo has demonstrated the ability to acquire through trade. Maybe Giolito becomes the right-handed Kershaw, Harper and Rendon become a 21st century Gehrig & Ruth, and the Nationals find the next Pujols in the draft. Or this could be it. Windows do close.