The Second Battle of Hoover Dam will not be affected by your killing of Caesar, the Legion will still attack in the same fashion as they do in any other style of NCR or Independent Vegas playthough. However, killing Caesar is totally possible, but killing him will only impact the Legion side of the main quest line. What happens if you kill Caesar before Hoover Dam? You have to get all the chems for the guy at the drug lab, and then do the oh my papa quest (75 speech required) once that’s done, your rep will go up to merciful thug and thus being able to start the Great Khans side missions. If you kill Jessup it is still possible to get your reputation back up.
Dead Sea, a member of the Legion in Nelson, will give you this quest. The first is We Are Legion, in which you must kill all the NCR soldiers in Camp Forlorn Hope. There are two specific quests you must first complete. Joining the Great Khans isn’t as simple as some of the other factions. The Great Khans will attack the player character if the hostages are engaged, so wait for them to leave the area. Killing them results in XP and Karma loss, in addition to NCR infamy.
