You can say the Leafs won't be able to afford him, but the Leafs will bend the cap rules backwards and forwards, sideways, up and down to keep him and the team competitive. Essentially, they'll hand him a blank cheque and fill out the roster by finding late summer UFA's the way Dubas has always done.
Matthews has said before he wants to bring a cup to Toronto. That's his mission. Maybe after he parades down Front Street, will he look somewhere else to sail off into the sunset, but it doesn't sound like he won't be leaving Toronto anytime soon.