New coach doesn’t even need to get extreme about it, let Marner play top-6 + PP like normal but run a system that no longer depends on him. Other players carry the puck in, someone else quarterbacks from the point, Marner plays like a normal hit and run wing instead of LARPing as a C.
Without his free system points he’s looking at a 70-80 point season without needing to visibly sandbag him. That hurts his next contract way worse than purposely torturing him with Kampf minutes where a GM will just ignore the results. A year of regular top-6 winger usage instead of running him as if he’s Kucherov is a realistic look at what he’ll bring to his new team, good luck with the 12+ demands at that point.