I have a question about the quest to recieve the M1 Garand "This Machine"

Can this quest still be completed when Isaac or Blake or Miguel are dead?

It would really help since I am a complete unique weapon junkie.

Thanks

I guess those three are part of the quest? I just hacked the sergeant's computer for proof, brought it back to Boyd - done and done. Didn't talk to anyone before that. Was actually a bit surprised to get a unique weapon, was just expecting some caps.

i was wondering the same thing, I dont meet the req to complete the quest, but just fig i try all possible outcomes and it is possible to complete with the NCR guy dead.

Try the Vault.com, this is the Fallout Wikia. You will find that this quest is bugged and by hacking the computer(upstairs in Contrerasas's area); you can turn him in to Boyd. She gives you the rifle.
Good luck