There's 22 free agents on the Leafs roster. Brad Treliving won't be able to keep them all, unfortunately. One of them is fan-favourite Ryan O'Reilly. He'll ask for a lot of money and unless he's willing to play for less money, he will change team when the market opens.
Yes, he isn't the player he used to be. Yes, he had a lot of health issues. Yes, he might retire this summer. However, there's a chance that he might want to look for another contract. Toews didn't have bad numbers last season, when he was healthy.
Toews isn't in a position to ask for a lot of money. He knows it, if he wants to play again in the NHL, he'll need to accept a lower salary. This is where Treliving and Toronto come into the conversation.
Having the opportunity to play for another original-six team, with extremely talented players, doesn't come around often.