I suspect the Rangers will be in on Panarin but not at all costs...if he wants top dollar then Florida or someone will give it. If he wants NYC while still getting paid a lot, then the Rangers have their chance.
He could theoretically still get paid top dollar (12 mill) in NY and the Rangers could fit him and Trouba (lets say 8.25 Mill) in if they:
Trade Kreider, Namesnikov and Vesey with little to no salary returning. This in itself shouldn't be much of a problem.
Buy out Staal - Shattenkirk's buy out value is basically nil in 2020-21 and Smith is waiveable to get maximum salary savings.
Bury Smith and Belesky
This would also require the team to bridge Buchnevich, DeAngelo and Lemieux, which isn't too much of a problem. By the time their next contracts are up they'll have a better idea of who they want to keep and who they can trade away. They should be able to get those 3 signed at around 7 mill all together.
Again, a ton of moving parts which makes me think its not really all that realistic, but it could happen.