Messi will probably not return to the right wing. We are in a desperately need of a Suarez replacement if he leaves or not. Currently we are lacking goals and this is not something that will change with Dembele back as he isn't a goalscorer.
The club needs to find a goalscorer who operates form the left wing. Mbappe would have been perfect for that role. I dont think Griezmann fits the criteria for this role but he is probably the clubs first choice to reinforce the attack. I would rather go for someone like Werner or Martial. They are not on Griezmann level yet. We could also consider a winger like Pulisic, Richarlison, Malcom, Leon Bailey or Julian Brandt. A forward line with Messi/Dembele and another winger would probably lack goals but Messi is best with two wingers playing besides him.
Next summer Julian Brandt will have a release clause of 15m which is a bargain in this market. He would add depth, youth and quality to our frontline.
Just hope the club will consider these options instead of going the "easy" way and paying 100m for a 27 old Griezmann.