If makarov died who would likely become guildmaster? Laxus? Erza? Natsu??? It seems like Laxus to me but would that mean gildarts would come back. Or something even crazier like jellal secretly being master? What you think?
Natsu would get the guild constantly fighting itself and bankrupt them with massive food bills
Ezra is the disciplinarian XD.
Though honestly in terms of how the story would progress... Probably Laxus as he is notably older than Ezra (more experience), is Makarov's grandson, and already has some Intel on things like the Lumin History or whatever it is.
The next Master will be Natsu. Because c'mon, Makarov dying. If he does, it'd happen near the end and he gives Natsu his will. And as soon as Natsu becomes the Master, he'll learn some bullshit "Fairy Tail's forbidden magic: Fairy Fire". And use that to beat Zeref. Why? Because Salamander, that's why.