So as a hardcore fan, I believe I can safely say for all of us that ROTF was definitely the worse of the three Bay films, so here is essentially how it should have ended making DOTM even more awesome.
What I would have liked to see is, as he is fleeing with starscream, Megatron was chased after, and stopped by Optimus Prime. They would have had an epic deal using swords, cannons and all that great stuff, and Megatron would die. For good this time. Starscream would then take over and be crowned, (again if you read some of the movie comics) and then I think that should have closed the movie, especially if it had a close-up of his face.
Then, after causing some havoc and resurrecting Shockwave, Shockwave would kill him and become commander. I think this would definitely have been a better version of the films, and one I would actually be excited about.
What do you think???