Curate, connect, and discover
Taking this post and adding my two cents:
In Age of Extinction KSI used Megatron’s head to code for their bots. Brains says something along the lines of “his head isn’t as dead as they thought”. Megs is able to pass on his consciousness to his new body this way.
Daytrader had Starscream’s fully intact head (even though it should be destroyed). With Starscream’s indestructible spark I say his head is all that’s needed to resurrect him. Megatron may have even known Starscream was still alive somewhere in there because he spoke to him.
Also
The Allspark can give so much energy and power for a nearly destroyed bot to completely reform a new body: i.e. Frenzy
The Fallen already stated the Allspark cannot be destroyed only transform. When the Allspark fragment mixed with the Matrix it became an all in one power source of the Primes.
Quintessa and Optimus both have the power to bring Starscream back. I think it may had been in the works to have him come back with how his head is somehow fully intact and Megatron just so happens to be the one to find him.
Thinking about this AU again
I just think it would be a neat way to bring immortal Starscream to Bayverse. Literally has his spark dragged back to living by Quintessa’s “ “ “magic” ” ” and now he can’t fucking die again, and he’s so TIRED, just make it end oh my god
Boring reason: Quintessa was just bringing back old sparks to rebuild Megatron’s army to do her bidding, but did not have time to do more that Starscream and a handful of others before getting her shit pushed in by Optimus.
Shippy reason: Starscream was brought back specifically in order to make Megatron easier to manipulate and control. Gets a brand just like Megatron and Nemesis, and she routinely makes him do things to keep Megs compliant.
Either way it’s fucked up and even after Quintessa disappears he’s still stuck alive and it’s Hell.