You talk as if the Toronto Maple Leafs are some franchise who doesn't even know what losing is like the San Antonio Spurs. We're shit and haven't won a playoff series for 17 years.
The team Dubas has built literally had it's best season in forever. They were good defensively, they were good offensively. They played well in front of their goalie.
It's not his fault if they choked. He's willing to bet his job that soon they will break through. He knows he's a goner if that doesn't happen. I don't see anything wrong in backing the group. I would want to trade Marner simply out of rage because he's f***ing sucked but what do you actually even get in return that will make the team better not only in the short term but also long term? I doubt very much.
At some point, the players need to look in the mirror and play to their capabilities and he's betting it will happen this season.
Like or hate Dubas, if you were a player on the Leafs right now, you would want to run through a wall for him (if you give a single shit about winning).
What Dubas is doing right now is exactly what you would want from a leader.