I think we'll see some players get bigger deals between now and then. Even if Buch is bridged now, he will need another contract in 2 years. The same goes for ADA and Pionk, assuming they are both still here in 2 years. Chytil, Andersson, Howden and Lemieux will all need new contracts. None of those guys will break the bank unless they take a leap forward in their development/production, but they will all get raises. And who knows what will happen with guys like Strome, Names and Fast.
On top of that, we will very likely target some players via UFA and trade who will make a significant amount of money. Those players could be potential core pieces like a Nylander, Kapanen or Trouba. They could be stop gap UFAs signed for 1 or 2 years. They could be cap dumps from other teams. We may not sign Panarin, but I don't think that means we won't sign any UFAs at all.
Let's assume in summer 2021 we have:
10 Forwards (3 slots still available): Zibanejad 5,35 millons, Buchnevich 4-5 , Chytil 4 , Lemieux 3-3,5, Strome 3,5-4, Andersson 3, Howden 2,5, Kakko 0,9, Kravtsov 0,9, 1st 2020 forward 0,9. 10 Forwards = 28-30 millions
6 D-men (2 slots still available): Skjei 5,25 millions, Miller 0,9, Hajek 3, ADA 4-5, Fox 0,9, Lundkvist 0,9. 6 d-men = 15-16 millions
2 G (0 slots available): Georgiev 3-4 millions, Shesty 0,9. 2 goalies = 4-5 millions
Dead Cap Hit; Girardi 1 million
It's all together 48-52 milions. The cap floor will be probably about 64-66 milions in 2021/2022. In that scenario we would have to spend 13-17 millions for the last 5 players (We would have 23 players in the roster but at least 3 of them would have to play many games in the AHL). It's possible but with almost 2,5 millions coming from buyouts of Smith and Staal it would be easier.
I'm aware the roster and the contracts values mentioned above are only my speculation (2021 reality can be much different, e.g we don't know if all of Chytil, Andersson, Lemieux, Howden will deserve for NHL in two years), but I still think the risk of cap floor problems is high in 2021. That's why I would buyout Stall and Smith this summer (It's safer in terms of cap floor and we have more slots for our youth since next season).