I think that plenty of teams would trade a good deal to get Gallagher, primarily futures if that's what Montreal really wanted, though I seriously doubt that the Habs' brain trust shares the OP's belief that the team needs to rebuild or restock the cupboard.
Notwithstanding the divisional quirks brought on by the pandemic, and the realities of trying to compete in a stacked Atlantic Division for the next few years, Montreal just made the Cup Final. They aren't going to sell off assets in their prime signed to reasonable contracts. This is true even if there is a reasonable chance that the Habs miss the playoffs this season, looking up at Tampa, Toronto, Boston and Florida.