You obviously don't blow it up. There is no circumstance where it would make sense to trade Matthews or Marner.
I think you have to give the kids a lot of opportunity. Sandin and Lilly should be penciled into the top 5, with opportunity for the significant top 4 Holl/Boosh/Gio minutes. Up front Robertson needs to get a real opportunity to play regularly. Knies should be penciled in for after the NCAA season. Guys like Holmberg, Anderson, Steeves, Abruzzese, etc should be given real looks, not 2 games here and there. The best bet at filling depth spots with talented players cheap is through the draft. By the deadline you'll know how many NIck Pauls/Gios you need to acquire to fill the spots the kids can't.
Use whatever process helped identify Bunting and Kampf to try to get another Kampf/Bunting. Forget spending money on vets like Ritchine and Kase to eat depth minutes. You can always get guys like that cheap at the deadline. I'd rather see what we have with the Marlies and accrue the cap space for the deadline where you can buy much more for the extra couple mil.
It should be a priority to spend Kerfoot and Mrazak's cap space better. Kerfoot is a homeless man's top 6 swiss army knife. You need someone in that role that can impact big games positively, and ideally can actually play center, for that money. The goaltending goes without saying. That was by far the biggest weakness of the team this year. This is where you can make the team significantly better.
I would be fine with moving guys like Tavares, Nylander, RIelly, but it has to be a deal that makes the team better. Just trading them for picks or prospects, or to make a change doesn't move the team forward. And those deals will be very hard to find. There are so few deals that would make sense, especially for Nylander. They can't afford to make another Kadri deal with a guy like Nylander or Rielly. They already tried the "trade a key player to make a change" move and it blew up in their faces. No one calling for "change" ever talks about that.
Muzzin is the more interesting question. Lots of reasons to move him and keep him. Its hard to replace what he could bring healthy, and hard to stomach another regular season like that, for that cap space.