The problem is that you think keeping Newhook will extend their window but it wont since Kadri is UFA soon and will get payed somewhere else. Avs have been lucky underpaying Mackinnon and Devon Towes but that wont last long so I would say strike while the iron is hot. Winning a cup involves lots of luck, and lots of depth plus a correct timing when the team is firing on all cylinders. Those opportunity only happens only a few times for an organization and Avs have it this year. Dont blow those opportunities just for the sakw of thinking you can "extend" the window in a salary cap world. Couple of years down the line, you might end up having to trade Towes or Rantanen because you cant afford to sign your younger players like Newhook. Just Ask Tampa
A quick rebuttal... the obvious counterpoint is that Newhook theoretically grows into that 2C, and is cheap (for the short term anyway). Most Cup caliber teams have ELC contributors.
In the interim, Colorado perhaps instead targets someone like Giroux or Copp, who almost certainly cost less, they still strengthen themselves up the middle (though I don't think Giroux actually plays much center anymore. I'm sure he *could* however)...
Point being Colorado doesn't necessarily need to splurge on a first line talent like Miller to push themselves over the edge. I'll again repeat how epic it would be if they did, but really they only need a capable middle six C (or perhaps a 2C if you're convinced Kadri will be naughty in the postseason yet again). They keep the promising young guy who then theoretically grows into an important piece down the road for future runs.
I would also add that I agree with the poster who pointed out they're sunk if Mackinnon goes down, just as most contenders would be in a pickle if they lost top talent. With the cap, you can't just go out and buy whatever because of what *might* happen. ie "Oh noes, we need Miller because our top line center might get hurt"....
As for moving Rantanen to retain Newhook on his second contract, come on. That would be like Tampa trading Kucherov so they could retain Cirelli. They'd find a way. Yes, maybe they move Toews, and they probably get a pretty good return. But now we're getting ahead of ourselves...