House Medici was expelled from power and exiled from Florence in 1493; they would return to power under Cosimo Medici in 1512. Your challenge here is, how can the latter be prevented with a PoD after the former? (Can it be after the death of Savonarola?) How long can the "people's republic" of Florence last, and can it prosper?
And given the answers here, what are the effects? On Italian geopolitics, European history, art history, etc?
EDIT NOTE: I was mistaken about the red highlighted section; see below.