Yes, there were 2 endings and you can see them on the DVD. Oddly the "downer" ending where he dies was the one picked for the theatrical release. However, the reason I didn't like it was that the whole thread with the girl with the butterfly tattoo and the zombie leader was just tossed out the window with that ending. In the other one, Smith backs off and the leader gently retrieves her and they all leave. Then Smith and the other 2 turn and run for the car and get out of the city. Everyone lives and the evolution of the zombies from mindless to intelligent is proven.
The theatrical one was more "oooh, he sacrificed himself in the end once his research was complete".
The Jedi Master
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Back off, man. I'm a scientist.