I'm a well read grad student who's bluntly honest about all things, although I try to be most honest about myself.
So much yes! Grimlock comes back, and of course, it's not quite how you'd expect, and it certainly doesn't end how you'd expect. It's brutal and far, far worse than anything I'd expect.
The Scavengers agree to find the Magnificence, for a whole lot of money. Instead, they find Scorponok, the Decepticon who used Grimlock, torturing him, experimenting on him, and it's revealed why it was done now.
Scorponok also has some control over Grimlock. And it's this fact that is truly tragic.
I was left astounded by the ending. Well worth reading!