If you noclip to the nearest void when nihilanth's "overloading" so you can escape the wrath of the trigger_teleport (to avoid getting teleported to the next level) then go back to nihilanth you can see that he dosen't die.Its no fake. I tried finishing half-life another time with cheats (preferably noclip) then when I beated nihilanth before the part where i get Teleported to gman, I "nocliped to the "void" and skipped the teleportation. Then when I went back to nihilanth he's not actually dead (there's even no death sequence for nihilanth), he's actually rotating with teh bezerking beams