It's a great concept
But you went on and on and on and on with the guy who had the cure for cancer, and it was pretty obvious what was gonna happen with him. We knew the bullet was gonna come and kill him and wipe out the cure for cancer at the same time. For that reason (plus the fact that he wasn't really killed in a funny or original way) the joke fell flat. If the punchline to the joke is known, taking longer and longer to get to the punchline doesn't make it funnier, it just makes it more tedious, unless there are little gags along the way.
Of course a lot of other people seem to like it, so oh well.