I understand why the gargoyle withered and died after its master was killed...but why did the zombie randomly keel over? Unlike the gargoyle there was never any indication his life force was tied to a specific individual. Otherwise, he would've died when Bordon died.
There's talk earlier in the film of zombies having a short lifespan compared to normal, living humans, but there's no indication whatsoever that Bordon's zombie was anywhere near the end of his lifespan. He seemed strong and virile as ever (esp. given he was the only one to remain standing during the explosive entrance of the Old One).
So...why did he just gall over and die? It's one of the few poorly thought-out decisions in an otherwise decent movie. It would've been far more amusing if he'd survived, and just remained standing there after our heroes departed, awaiting orders that will never come.