If I recall correctly, it's been over a year since I've watched CB, Vicious always said that Spike could never die, because only he could kill him. and vise versa.
What I got out of the ending was that neither could be killed by anyone besides each other. So when one died, they both died.
That's my take on it atleast.
He only managed to get a few shots to the shoulder, stab to the shoulder, shallow slice to the thigh, and that's about it...
Again this is from memory, right at the end Vicious delivers a fairly deep slice to Spikes abdominal area, which probably hit some organs.


