When is it appropriate to discuss death with a child?

Qu

Not really a rant, just not sure where else to put this topic. My husband and I agree on most everything, but this one thing we argue over. My mother in law recently had a cat pass away and now my daughter, she's almost 4, has been looking for the cat and wondering where she is. Now, I want to explain death to her, my husband wants her to stay innocent about it. My problem with that is what if something happens to me? What if I get hit by a bus tomorrow? Is he just going to tell her I went to heaven? It's been a long time since I've been my daughter's age, but I just know my 4 year old self would be wondering why mommy didn't take me with her to heaven or why I couldn't visit. I feel like that would be psychologically damaging to a young child. I'm just so confused about this.