It may in fact be that Bergevin is MINO (Manager-in-name-only), and that a new GM will come in with a fresh slate once the harder parts of the rebuild are completed. But the Leafs did that properly. They traded away Kessel and Phaneuf. Let me know when the Habs trade Price, Weber, and Pacioretty.
It is the case that coming in right now would suck for a new GM. The Habs will not be winning anything for several years, and the division is getting stronger. This may be much harder on the next GM than it was on Andre Savard.
But if they can clear Price, Weber, and Pacioretty, possibly Shaw and Alzner as well, and have one more tanking season, then it's not all bad for the next GM. However, it will still be very hard, as it will be very hard to transition the team to being good.