In an interview, Lorenzo de AceVentura (idkwtf his last name is) said that Bumblebee and Optimus would be the obvious ones returning. It has also been confirmed that Shia and Rosie won't return. My point is, why would Bee be in the movie if Sam isn't? He's got the whole guardian thing that he has to attend, but he can still chill with the rest of the Autobots? I'm not saying it's a surefire thing, but it can be done. Of course it's possible that among the stragglers on Earth, a leader arises. Sure, some random Decepticon from space somewhere can show up with his army. Maybe Unicron can show up and revive them all (but that'd be a total cop-out). I'm just saying that it is increasingly possible that TF4 will be a prequel to the movies, showing either the Great War or the Final Days of Cybertron before everyone jumped ship. I know they wouldn't get their oodles of Chevy sponsorships, but still. I know I would actually prefer a prequel, since I am completely tired of the humans' screen-time. I would also love to finally see some Cybertronian Alternate Modes other than Megatron's "Armjet" from TF1 and tank from TF2. Also: we would get to see Jazz again! Huzzah! Possibly even a young Jetfire, or heck, even a talking Bumblebee (without the Alfred Pennyworth voice).