The speculations of Messi's return to Barcelona are now hitting up and it seems likely that a move can happen in the summer as Barcelona President has mentioned that the club is talking to Messi's camp and discussions taking place already. I think Barcelona is also putting in place measures to satisfy every financial fair play rules if Messi is to join eventually.
The Barcelona camp actually believe they can pull this off. It will be a good deal for them if they get Messi back but its going to be a very difficult one. The good news is, Messi actually wants to go back and he's ready to make all the sacrifices for that to happen. I read at article that said Messi is ready to adjust to the financial constraints of the club.
Signing Messi would be good for Barca but only in the short run. Right now they've made quality progress in trying to rebuild their team without Messi and learn to play without relying on a single player, if Mess comes back I think they'll be taking a step backward after taking two steps forward. Don't get me wrong, Messi is an exceptional player and nobody can do what he does on the pitch even at his age but bring him back will halt their progress because the team will now be dependent on him ones again. And since he'll always deliver, it won't be felt in the short run but in the long run they'll feel it.
To avoid that, Barca need to also pay attention on other part of their squad that need strengthen.