Getting Messi back would ruin everything good we have done so far.
No player would benefit from him coming back, they all would again have to sacrifice their game to run and cover for someone who will walk for 90 minutes while playing every possible game. He is not worth it anymore to center all the play around him, he doesn't offer enough moments of magic to be worth it.
And in this modern age, even one player walking, means failure in the CL against top opposition.
He can return for one game to say godbye to the fans and thats it, everything more than that would be a huge mistake.