I think you might be right. Marner most likely getting traded.
Tavares would be the obvious choice, but for numerous reasons that's not going to happen.
Matthews shouldn't be dealt.
Nylander is a fair contract now and not a burden.
Marner looks like he's the overpayment and seems to take the most heat.
Unless a team overpays, the trade when it happens will be a loss for the leafs. However they're likely to get futures and cap space, which if developed and used properly could be a huge haul with the player(s) under contract they get in return