Sure, old lady Gibson can repair unless you chainsawed her too lol.
I'm sorry I'm having fun with you but I really laughed hard at your post.
Seriously, can you walk up to the NCR npc's and have a dialog? If you can that means you can do their quests and everyone of them will get you fame and eventually ya'all might become freinds again.
The Reputation system dosent work like that, once you start killing you cant fix it. e.g. You can be Idolized by the NCR, kill a few people and you move down to Wild Child, you cant move back up. It's not like 0 is neutral, 5 is good, and -5 is bad. It measures good between 0-14, and bad the same way, they arent on one scale.