In the end, Grand Rapids was dutifully cleaned up, with help from both the humans and the relieved Transformers. The army and the Autobots were able to cooperate and make a treaty, with the army saying they'd leave the Autobots alone if the Autobots would help them out with any Decepticon threats that might come in the future; the Autobots agreed to these conditions as long as KSI was disbanded, and that they wouldn't be involved with any human affairs. The two Newborn Sparks were living separately with the Yeagers and the Runners, though the Runners were hesitant about letting Transformers into their home. The Autobots separated and went their ways, being sure to keep in contact with the separate families to check in on the Sparks. Jigsaw took on the form of the Runner family's 2006 Acura MDX, the car that Mary Runner would soon start driving in order to let her dad have the Toyota back.
For the last time the Autobots met outside the city of Grand Rapids. Standing there, on the edge of the Grand River, they saw the efforts they had made on the city's rebuilding. A roar escalated from Grimlock's throat, followed by roars from the other Dinobots and from Clunk.
"Are you coming?" Megatron asked Unicron.
"I'm headed out with the others to - in the very least - update my form. I'm asking if you want to come along."
Unicron shook his head. "Unfortunately, I can't. I have one last chore to take care of. You guys go on ahead."
He watched them go, murmuring softly to himself, "My brother has hailed me. My time upon the Earth is over. Protect his children, as I will no longer be around. But first! First... I must go pronounce sentence upon the enemy."
He walked away from the sunset, leaving the group walking into it. Clunk slid back into the waters of the Grand, whipping his tail back and forth to power away into the murky depths.
Deep among the fiery furnaces of the hellish region known only as the Pit, the furnaces were continually filled with coal to keep it burning hot. In one of those coal piles belonging to the biggest furnace, Powertron woke up. He couldn't figure out where he was at first. Then he saw the door slam shut, and watched as the flames started to surround him again. He started screaming bloody murder, pressing against the furnace walls, trying to escape.
Outside the furnace, down upon the Earth, Unicron stared down at him. "Your destination is hell's furnace, as I have told you before," he said. "Now it is time to pay for the unspeakable crimes you have committed. You will never escape the torture you gave to others. Not while I am around. You will never know freedom from the pain you gave to others across the divide of a lust for power and the crashing down of it when everything you've done has failed. Taste failure. Taste it for a thousand years."
He watched as the gaping hole closed, leaving the burning Powertron to suffer in the Pit. He strode across the area to the last part of the helm of Powertron's head; the Dark Spark lay nearby. He picked it up, studying it carefully. Then - without warning - he heaved it into the air and cleaved it in two with a blade shooting out of the back of his wrist. The two chunks of head flew through the air and fell into the river. The head now disposed of, Unicron now turned to the Dark Spark. He picked it up and looked at it carefully, trying to think of what to do with this deadly material.
"It's best that nobody knows of this at all," he decided. "Time for this to go away. Permanently. And I know exactly where this should go."
He wound up like a baseball player and chucked it outward towards the Great Lake Michigan, allowing it to fall out of his sight. He could hear the screaming of Powertron down within the Pit, and while listening to it, he sprang into the air and glided up to the stars, completely aware of Powertron's roars.
"I WILL RETURN!" Powertron wailed.
"Not unless you want to die at the hands of my brother, you won't!"