I really can't imagine a scenario that has Gardiner staying even if he does stay at the AAV for reasonable term.
Matthews, Marner, Tavares, Rielly, Andersen, and Nylander is the core and outside of those 6 players every penny needs to be spent wisely.
Kadri, Hyman, Muzzin, and Dermott make up a layer of quality, reasonably priced support players beneath that core. Marleau's experience may or may not be needed going into next year depending on how this year goes and considering we now have Tavares and Muzzin; obviously a 6.25M cap hit is too much, but he does bring a nice ingredient to the recipe and you can't just solely look at his on-ice play as he contributes off the ice as well.
Kapanen and Johnsson need to be resigned at reasonable figures as they are also key support players.
All of the above support players offer us a lot of versatility; special teams ability, defensive acumen, depth scoring.
Gardiner is a good player but proven to struggle in big game situations. We want to be in game big situations and big game situations are what actually matters; we will make the playoffs with or without Gardiner. Do we want to have a liability playing high up in our lineup in a game 7?
We have LD depth of Rielly-Muzzin-Dermott which is excellent, with Sandin as a top tier prospect in that position. We can't afford luxuries and Gardiner would be just that; we don't need him, and he could end up being a risk in big game situations. We need to be wise with the money we do have.
Obviously I am not privy to all the trade scenarios/FA options Dubas has/will have, but I really can't see Gardiner being the best fit. In a perfect world, Zaitsev finds himself, Liljegren steps into the 3rd pairing, and we add a Pesce-esque player; if not, we move Zaitsev, add a Pesce-esque player, add a stop-gap to hold Liljegren's 2nd pair spot for a few years (a Ron Hainsey type but ideally right handed).
We need to be wise with how we spend every penny outside of our core. Gardiner is not a very good option in that regard.