That kind of trade just isn't going to be available though - and Marner's AAV would make any similar move very difficult for the acquiring team. I mean, if they disappoint, maybe you move Rielly but then are still left with a gaping hole on defense.
The Leafs have a talented core. Like it or not, this is likely the roster they're going with for the next 2-3 years. Even if they disappoint in the playoffs, there won't be a blow-up. It'll be like Washington, St. Louis, or even Tampa. Just keep going for it, keep the core intact, make some good tweaks around the edges, and hopefully you make a breakthrough. Hockey is a big crapshoot.