This is what I think too. They were "all in" mentally and they got it done. It's only natural that they:
1. Want to think about life where they aren't under constant pressure to perform
2. Aren't in any hurry to commit to putting that pressure right back on themselves (and then more. Because teams will be gunning for them).
Ultimately I feel like they will be back though. Not only do both of them eat sleep and breathe football but they just want to championship. They could go into next season feeling a great amount of relief that they've already accomplished their mission. Like they're playing with house money at this point. Ultimately I think that Donald and McVay and Von Miller stick around until Stafford's new extension is up.