With the Werenski deal and now the Nurse deal at 9.25m, the writing seems to be on the wall when it comes to Rielly. He can easily command 8m on the open market and Toronto has no business paying him 8m+
Toronto is going to be in a tough stop, try to keep him for another run (whether you think they can win is another story) or sell him off right now and get good value on him (could be more if they have an extension in place with the team, like Jones and Chicago.)
Even if you can get a 1st + good prospect or a roster player, you could always turn around and flip the assets for another d-man with term.