If one can define them with the phrase "bereaved parent" why couldn't one define them with a single word?

How do you define a parent who had one or more children that all died? Are they still a parent? A childless parent? Do they "have any children"? How would they answer the question? "none living?" "No" "yes, but they're dead"?

I don't think a term to describe a bereaved parent ould really need to specify whether there were other children or not. A widow can have a husband - if she re-marries she's a "re-married widow" but still a widow. An orphan can have parents - they can be an adopted orphan. And a parent who's lost a child can still have other children but be bereaved all the same.