I can't imagine they see Alvarez as more than a stopgap to take September starts away from young pitchers who do not need the innings. He'd be arbitration eligible still so I can't imagine they will keep him through the winter. And once he is a free agent if scouts do see something they like there is no guarantee he would stay with the Phillies.
Not that he was that good today anyway. Even if they bring him back it is probably to shore up the AAA rotation.