Latest playthrough, I couldn't even get the Echo option. There was no Int check and no option to have Edwards rejoin Astor's team. After a lot of reloading and redoing the quest, I finally got him to give the line about going to Echo, so I concluded the quest that way.
Fourth playthrough, I had installed Dead Money, and suddenly, Astor wouldn't give me any dialogue other than that Edwards should be put down. Second playthrough was Legion, so didn't bother with the quest. On my first and third playthroughs, I had no problems getting Sgt Astor to accept Edwards (passed an Int check to say Edwards wasn't feral). I generally enjoy playing more empathetic, helpful characters, so try to get the best outcomes on most of my playthroughs.
I've played through FNV a few times now and have hit a problem with our ghoul soldier friend.