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.
I don't think it will work, looks like messi will still have one more season to go before he actually retires. if barcelona are planning to facilitate messi's return to camp nou, just to become a club ambassador, or as you say as the new coach of barcelona.
I assume that won't happen. if the scenario is as you say, in other words Xavi will be replaced. Isn't it Xavi who wants Messi to return to Camp Nou, there are a lot of rumors going around. but for sure, messi still has a chance if he still wants to play one more season with PSG. PSG have the option to extend Messi's contract for another year.