I think it would be interesting and a nice subversion of the usual Transformers formula to tell a story where Galvatron eventually turns back into Megatron.

It would begin after most of the events you would expect from a typical Transformers story have already happened. Cybertron was devastated by the Great War, the Autobots and Decepticons brought their conflict to Earth, humanity became involved, and the Autobots ultimately won with the help of their human allies. By the time the story starts, the Autobots are once again in control of Cybertron and have established peaceful relations with Earth and several other worlds.

The Decepticons, meanwhile, have been reduced to scattered remnants of what they once were. Their only real source of leadership is Megatron, who was reformatted into Galvatron and lost his sanity. With Galvatron as their leader, the surviving Decepticons become more of a recurring nuisance than a genuine threat to the Autobots, largely because Galvatron is too unstable and unpredictable to rebuild the Decepticon cause.

So the status quo in the beginning would be similar to the third season of the original G1 cartoon. Over time, pieces of Megatron's original personality would begin to peek through Galvatron's madness. Eventually, through a series of events, Galvatron would fully revert back into Megatron, but keep the power he had as Galvatron.

There should be a story where Galvatron turns back into Megatron