What do you think happens to the engineer after Sgt. Johnson talks to him one on one? I think he is still alive and well and serves the UNSC by repairing their vehicles and machines.
I think he’s of more use than simple mechanic, he could be intercepting and translating covenant comms, teaching ONI more about the forerunners, possibilities are endless but I would like to see him return in someway, nice little nostalgia always worked in halo 
He’s probalby being used and studied by ONI.
Edit:
> If you read Halo Glasslands, there are several hints at the fates of certain Engineers ONI had captured.
After now reading Glasslands ^this is correct.
I forgot all about ONI yeah ONI probably has him lol
> I forgot all about ONI yeah ONI probably has him lol
I wonder if he would be better of with ONI or better off with the Brutes. Could go either way.
> > I forgot all about ONI yeah ONI probably has him lol
>
> I wonder if he would be better of with ONI or better off with the Brutes. Could go either way.
I don’t think ONI would strap bombs to an asset that valuable, so VIRGIL is definitely better off with ONI.
If you read Halo Glasslands, there are several hints at the fates of certain Engineers ONI had captured.