If Mess comes, I think he takes Gundogan's spot as one of the two 8s in that case we almost always have to play Godsn Gabby and Bernado as the front 3 so their press can make up for the lack of press Messi will come with.I don't see Messi taking Mahrez' spot tbh, Mahrez plays wide right for us and even though they are similar, I thinik Pep sees Messi in more central positions as he has been playing lately.
Most likely in the false 9 role, Mahrez has almost never played there.