I've interpreted the OP's thread to ask - what should the Leafs do that next season's deadline if they know both Phaneuf and Kessel plan to walk?
At that point, you tangle them, and you tangle them hard, and hope that you get something of decent value in return - but you don't hold your breath. Simply put, teams will know that they can have a crack at both players on July 1st if they opt to leave.
The time to trade Phaneuf and Kessel, if there was suggestion that they aren't coming back, is now, or at the very latest, very early on in the season.
The trend lately has been a relative decline in the quality of both player and prices for the rental market. I wouldn't expect teams to give up much for 2 potential rentals, and I wouldn't expect teams to give up much period for Phaneuf
Target Vanek, Thornton and whoever else is available, once Thornton is signed trade Bozak for scraps and sign more UFA's
Vanek is going to Minnesota and Thornton will be going to a contender. There is a large bi-polar segment in Toronto ( who are more into theatrics and overrate marginal players) so don't expect top guys to come unless we're contending.
In other words, we're going to be entering tank mode if this were to occur. Maybe that gets us the cup in the future, but it'll be a slow process.
If we keep or lose either of them I think Joe Thornton, Vanek and Girardi should be the prime targets for us. Girardi is the exact type of Dman we need to pair with any of Dion/Gards/Rielly actually. Stout defensively, dependable, no injury history, physical at times. Right now I am curious to see what happens with Pietrangelo more than our guys to be honest.
I cannot see Vanek going to Toronto just a much as Parise, Suter, etc when they became free agents. Thornton spent much of his career in San Jose and with their depth, I doubt he'll be moving. As for Girardi, he'd be executed if he came here. The Rangers arguably have the best goalie in the NHL and had a very effective defensive system as well.