There comes a time where self PRIDE should come into play.
If I had a locked in guaranteed contract that allowed me to play out the year, but the organization came to you and said we would like to go in a new direction, and despite respecting your past contributions you're no longer apart of the future plans, using the teams lack of success as the reason to force change, you would think "being wanted and needed" played a part in future destinations and future employment.
Marner's lack of playoff contribution doesn't really give him a strong rebuttal case that he should be part of the solution and not viewed as part of the problem, due in part to his large contract impacting team depth. Marner has scored 11 playoff goals in 8 playoff years and 9 playoff series, averaging approx. 1 goals per series. You don't need to be paying a player $11 mil to get 1 playoff goal annually on average.
A team willing to trade assets for and willing to meet his contract demands beyond this one, considering its likely to be his BIGGEST of his career should play a large part in how much weight he places on his NMC to force Leafs organization hand to allow him to play out this year in Toronto. IMO
Free agency is a lot less certain as many players find out.. Many players have even forced their way off of current teams over $$ and demands despite being in great positions, only to find out the grass is not always greener on the other side. If Marner says I'm looking for $12.5 mil on my next deal and Toronto says. that is not happening here, then best start planning how to make that happen and the sooner the better.