Intense. Felt slightly bad for Billy. Though thats what you get when you hang around with a known nutjob.
My interpretation is that he IS indeed Nicolas, his feral personality was born out of distrust after what Martin did to him (doesnt want to sleep, when he sleeps he goes into super mode).
As for his death... Dunno, we see his face getting saw in two, limbs too, and I think I see two corpses lying there in the last panel. Its a terrible ending but I buy it.