Spike Witwicky spends his nights asleep in Optimus's cab now: the only place he can reliably rest anymore. His oxygen machine puffs at regular intervals, barely noticeable; the bracelet that monitors his vitals sends its data both to the nearby hospital and Optimus Prime's personal comm suite. He doesn't know how to interpret all of that data, but he's been taught enough to know that his friend is dying.

Their lives are so brief. Organic matter only holds together so long. Part of Optimus wants to try to find that machine that had transferred Spike's essence into an Autobot frame once - but the experience had been a traumatic one, and Spike wouldn't thank him for it. I've had a good long life, he'd tell anyone who asked. I've gotten to travel the galaxy, meet some interesting people - and I've had the best family in the universe, both human and 'Bot. I'll go to my rest with a smile on my face.

And once, when it had been just the two of them - Do you think we'll meet again, someday?

Seeing Spike smile wistfully, what else could Optimus have said? Almost certainly, my friend.

Stars are born, forge the makings of life in their bellies, explode and recombine. Optimus knows that cycle well. So, someday - eons from now - surely the stars will return his friend to him.

(aaaa help i made myself cry)