Yikes. I didn't kill Moriarty, but I did blow Mr. Burke away with the help of Lucas Simms (had to act quick though Simms has a glass jaw).
Wait a minute, it's possible to save Lucas Simms!? After reloading my quicksave several times, I concluded that Lucas dieing must be a scripted event, if you choose to have him confront Burke. No matter how quick I was, I never could save Lucas.