If and this is a BIG IF Treliving decided that he wanted to move on from Marner, and attempted to work around a NMC is to inform Marner that after next year the Leafs will not be offering him a new contract and using his money/cap space on a replacement player(s).
Marner using his NMC as leverage not to be traded, but that only applies while under contract. However with the thought that Leafs would like to move on, then perhaps he might be more agreeable to accept a trade to a team of his liking, and one that would want him, and willing to accept the terms of his next deal.
A re-sign and trade potential situation being orchestrated by Treliving here.
Without any trade even if Marner refused, then walking away from Mitch at age 28 (June 2025), does re-capture $11 mil dollars and that could be used on another UFA like say Mikko Rantanen, Leon Draisaitl both age 29 for similar future amount you might have had to invest in Marner and change the core., or of course use it towards pending UFA Dman like Provorov, Slavin or Theodore etc etc.
PS. Since Matthews and Nylander have both been re-signed by the current GM implying desire to maintain then to change the core 3 process of elimination makes it Marner the one on the move.