I did work with hospice patients before I die. Everyone thinks my attitude about death is callous except for the people I was helping to feel better as they were dying. They appreciated it, and hence liked me. But sometimes saying "It's OK that people die" isn't what family wants to hear. I seem callous, put the clients appreciate someone who doesn't treat them special because they will die soon (that makes them feel already dead and like they are defined by their dying.)
You are not apologizing for your joke. If humanity was more evolved, you wouldn't feel like you had to apologize for anything except a really lame joke. You are apologizing because most people are so deluded they are all afraid of dying and you did not give the people's fear of dying the superstitious awe they demand. And because most people are so insistent on enforcing their superstitions on everyone else that your lame joke threatens your business partners. You are saying: "I'm sorry I didn't adequately say what the consensus reality demanded of me." The next step for you (besides getting much better jokes) is to learn how to manipulate people's perceptions in consensus reality to control them instead of just confronting tranced people with reality accidently. Further, any publicity is good publicity. Apology not needed or accepted.
You should of seen me after Tim Russert died. I was gleeful. People die every day. If you're anxious about that, you can't live your own life. Fear of death is one of the main reasons people unknowingly live lives of quiet desperation. Using humor defeats the fear.