I'm not sure it would be a good strategy, what with some people harbouring the notion that the Leafs are contenders this year, but I do think it would be a fairly justified one for Dubas to call Marner's bet on not playing this season or playing in Europe. Yes, what happened with Nylander last year was ugly but I feel like the idea of Nylander playing in Europe was more of a thing he'd have been ok with. Likewise, if the end result was a Leafs trade, I think he'd have been fine with that too.
But if the Leafs don't like either the three year bridge Marner's group is proposing or the amount it would cost to get him signed longer term...wait him out. Sure, it could cost the team a playoff spot but realistically as sports fans we should be prepared for any of these guys to be gone for the year at a moment's notice due to injury. If Marner skips a year, it seems unlikely for him to ever make up the missed money on future deals and it would almost certainly ruin his relationship with the club. I feel like that puts Dubas in a pretty good position on November 30th.