The "obligation" is the possibility of losing him for nothing if Marner refuses to waive. The Leafs generally avoid risk.
Caught between a Rock and a Hard place.
If Marner refuses to waive then Leafs management hands are tied and only options are..
1) Allow him to become a UFA and then uses recaptured $10.9 mil cap space on replacement players via UFA signings or other means.
2) Offer him a future contract that Marner would be willing to sign (with an implied raise) and also having future NMC clauses, essentially doubling down on a situation they would be attempting to get out of by wanting to trade him.
Can't see how Marner's next contract demands other then a sign and trade agreement to his next team now, that would make both sides happy, where Marner gets $$ and Term he wants and Leafs get to move on and rebuild the team without him as their vision takes them. The "risk" portion is the same to MLSE as Marner saying I refuse to waive my NMC as that only leaves option #1 walk away if they want to move on from Marner now.,