Some people believe he might have already been traded last summer if not for his full NMC. That no trade clause guaranteeing he remain a Leaf unless he gave consent to allow them to move on.
When Marner was an RFA he threatened Leafs management with an Offersheet forcing Leafs management to overpay him to keep him. But he never officially signed it, an indication he never intended to leave only exploit that to his financial gain.
If he once again hopes to remain a Leaf then he is not being forced to sign with another team this time around either as a UFA, and instead should plan on having the playoff of his career and once again force Leafs management hand to meet his demands based on the merits of his contribution.
Point being Marner controls his future and at present NOBODY is forcing him to leave the organization and he controls that even when this contract ends.. However there is one thing perhaps preventing him from being life long Leaf and that really depends on his playoff performance and IF he accepts a contract from Toronto should that be offered, but on their terms. That offer can increase with a successful playoff season for the Leafs, that might not be available today until he PROVES it.
If it’s really only about the MONEY and Marner chooses to leave to chase top $$ then he was really only using the Leafs as a bargaining tool all along for his personal gain. Loyalty is a 2-way street and Marner is currently in the drivers seat.