So Megatron is dead. What if we had a character that was somewhat obsessed with Megatron to the point where this character is a force to be reckoned with. He could worship Megatron so much that he essentially becomes him and knowing that Megatron is dead takes over as leader of the Deceptions. The thing is here is that they can use Galvatron as a means to reboot Megatron's character which was a little underwhelming after TF1. Megatron would more or less be spiritual successor to Megatron and the writers can do with him what they should have done to Megatron - make him a suitble rival.