I think there is a small possibility that Matthews could leave Toronto and sign with Arizona, but it is very unlikely because a LOT of things would have to happen, and the Leafs would need to make some mistakes along the way. If the Leafs give him what he wants in terms of money, don't ask for any kind of a 'home town discount', all of this goes away this summer.
The ONLY way he could leave would have to be all (or at least most) of the following:
-Matthews isn't wowed by the leafs offer this summer, and decides to negotiate with them for something better and that drags on.
-The Leafs WIN the cup this year. I think Matthews would ge more likely to leave if the Leafs win, he can hold onto his 'hero' status here, be a cup winner and then go home. If the Leafs dont' win the cup, I actually think that bodes better for him staying.
-He has to know, of have it communicated to him somehow, that the Coyotes are going to make him the HIGHEST paid player in the league by far with a long term deal, make him the face of the franchise and he would have ample marketing opportunities waiting for him upon signing there.
-Whenever this spring the voters in Arizona vote for or against the proposal for that $2billion+ package including a temple of a new Arena, that gets passed and would be open/built in the prime of Matthews next contract.
-The Coyotes have to get better, now. They finished last year with 57 points. This year they are on pace for 65 points. If they can finish with 70 or more this year that would help.
-Matthews either already loves the Arizona Coaching staff, or you basically let him know he is going to be instrumental in choosing the next coaching staff.
-Arizona Wins the draft lottery this year, or at least picks in the top 3 and gets a great, nhl-ready prospect.
Is all that likely to happen? Nope. Can Toronto make it a moot point by not low-balling him or asking for a home town discount? Yes they can. But, if ALL of the above happened (which isn't likely I know), I think the idea of him signing in AZ is not out of the question.