How's Dubas fits the team under the cap before the LTIR occurs, which opens up 12 million dollars with Horton and Clarkson full time and Demott and Hyman part time.
You can apply for offseason LTIR, so no need to put either until Mitch signs (Clarkson was brought in to be able to allow the Leafs to negotiate through the season/be able to match a fictitious offer sheet).
It's complex especially with signings that go into the regular season, but really what is the concern. There is cap relief for LTIR players and especially for 10.6m of season ending players.
But really it's not like the Leafs are getting a unique cap hit of 90 m for "active" players. Depending on the Marner figure, the Leafs still might have to make a trade to be cap compliant.