Idk why but I think it's going to be Allegri. Messi is fed up and wants to win, they need someone successful who will command respect and Bartomeu is desperate for anything that will vindicate his rein. If he goes out as the president who handed RM the title, lost Neymar and Messi etc. he won't be able to show his head in Barcelona anymore.
They have a team that suits Max's 4312. Messi in that space between midfield and attack would finally be the tuttocampista he wanted Dybala to be.