I just beat the game aligned with the NCR.
SO! As I come to fight Legate Lanius at the very end, I'm scrambling for ammo and eating all the food in my inventory to heal myself (I decided to go finish the game while totally unprepared with 2 stimpacks, 0 doctor's bags, and only a couple guns I was carrying I actually had ammo for) along the way to Legate's Camp. Well, lucky for me the last NCR Veteran Ranger who died at the Camp with me had a Brush Gun and 20-30 bullets for it - more than enough ammo for me to finish the game apparently.
After I speak to Lanius and end up having to fight him as I don't have a Speech/Barter of 100.. I start backing up trying to recover from my crippled torso and head causing my vision to blur. I take a couple shots at Lanius through VATS and what do you [censored] know. Miss Fortune (who's super buggy for me ANYTIME she shows up - causing me to be stuck in VATS while being attacked or just not even shooting opponents, etc.) shows up to shoot him down.. but instead.. he flies into the air and for some reason explodes into a ball of fire. Legate Lanius is a [censored] phoenix.
However, he didn't die immediately it seems. He never came down to the ground as far as I could tell and the quest didn't update to tell me I had defeated him until I finished killing his 2 body guards plus whatever other Legion douchers were attacking my drugged up, dog steak eating, crippled head self.
Moral of the story.. Legate Lanius is a [censored] phoenix... or is it that the Miss Fortune perk blows and is super buggy? You decide.
toodles