That's a fair question and probably a good way to look at it.
Why do we keep them together? One answer could be that players develop and giving up on them early is often a big mistake. Stamkos, MacKinnon Pietrangelo, Ovechkin all took a long time before winning a cup. Kane, Toews and Crosby did it quickly of course. That was long ago though.
It's hard to get value trading a star player. You never win a trade when you trade a quarter for two dimes and a nickel. However, maybe it is not about winning a trade. Maybe it should be about making ourselves better. It might be the right move to trade Nylander for a second pairing dman and a middle six forward that have lower cap hits and a few years of control. In this case we upgrade the D, take a hit on F (hoping Bertuzzi, Domi, Knies and even Robertson can fill that gap) and we add cap space...not so much this year but next year when Willy's raise kicks in. I don't know if such a trade exists. I have been wondering if Oleksiak + Wright is a move they would make in Seattle.
Waiting for JT's contract to end is an interesting discussion. It does not mean he leaves necessarily...it SHOULD mean he stays, at one hell of a hometown discount. This is LITERALLY his hometown (remember the PJs), he has made a tonne of money, that money (+Covid flat cap) has handcuffed us a bit, and he is our captain that wants a cup. I am thinking closer to Gio or Spezza on his next deal. 4 x $2M? That would be great value and a real asset. I would not want a Malkin deal where he is still $6M on our cap.