The big speculation is that the Autobots are gonna leave Earth on a modified space shuttle. Starscream left Earth in the 1st movie. Megatron left Earth the second movie. The Autobots talked about leaving Earth the 2nd movie. The Autobots flew to Earth the 1st movie- likely with the intent of locating the Allspark and leaving again. So why would they all of a sudden need assistance getting off this rock?