How do you explain death to a 3 yr old?

Not so much death but my father in law recently passed away and my daughter was close with him. She hasn’t yet asked about papa bc she thinks he’s still with the doctors. What do I tell her when she does eventually ask “where’s papa”?

We don’t talk about God/heaven we aren’t religious so tbh if I say he’s with God she probably wouldn’t understand what I’m talking about but I guess it would open up that conversation