Although that part with Simmons in the wheelchair looks like the end, its probably not. They probably did it to lead us off. I think its somewhere in the beginning after OP is mad at the humans and decides to go away, says goodbye to Sam ( still dont know why Simmons leg is broken). Bumblebee stays and when the DECEPTS enter through the space bridge he sends a message to OP and then all HELL brakes loose... or something like that
Ya, that makes sense, although if Optimus is mad at them (The Soviets?) for what I think he is (Hiding Shockwave) then... That doesn't seem too leaderly to leave a planet with someone like him on it.
Oh, and I noticed something else. (probably me just not noticing the obvious) When that light or space bridge or something appears and seemingly "wakes up" the moon 'cons, they're already there. Which brings the question: What was that?