This is just an idea. What they should have done with the Fallen is after the Sunharvester is destroyed he leaves Megatron by himself to die, which pisses Megatron off... So in.the sixth film, the Fallen could return with Unicron (they join forces) to finally kill Prime and destroy the earth, but Galvatron (who has Megatron's memories) recognises The Fallen and wants his revenge for leaving him to die. So then we'll get Optimus and Galvatron vs The Fallen (which leads to the Fallen dying) then have unicron take over Galvatron's spark/body, so we'll get Optimus vs Galvatron (which leads Galvatron to be badly damaged) then we'll have all the Autobots vs unicron! Optimus destroys unicron, and when everyone is happy cheering, Galvatron gets a cheap shot at Optimus which kills him. Then Bumblebee finishes off Galvatron! The Fallen is too strong of a villain to be in.the second film of a (possibly) 6 film franchise. It's kind of random as well.