The possible thing is he may come back to the barcelona but with different status. he may come back to the barcelona as a coach rather than player pretty much the same like what xavi did. Xavi was coming back to the barcelona as a new coach for barcelona rather than become a player again. So many speculators have been saying this thing many times. Im not even thinking messi will back to the barcelona as a player.
His old will become too older to compete in the la liga. I think that would be a good thing to see him as a new coach for bacelona.
Yea. Returning back to the club as a player will put the club under so much financial stress which is what they have been trying to resolve. Besides, times have changed as well as the squad. Anyone who thinks that if Messi returns to Barca there's going to be a good rhythm between him and Lewa and that he is going to fit well with Xavi's tactics is only day dreaming. Just as the user above said, he is likely going to return in the capacity of a management staff. That will be suited for him.