Should parents have legal standing and the ability to sue for damages in the event of a wrongful death of an **adult** child? Key word: "adult", age 18+
I say 'no'. An adult is, or should be considered, a separate entity... emotionally, legally, and otherwise... and should be treated as such. The ties have been broken, and there is no longer a direct connection.
Lone exception: If the parents end up raising the adult child's children, then the parents could sue for the costs of raising said children, but no other damages, emotional, punitive, or otherwise.
Please note that this question is not asking what the current legalities are, but rather what the legalities should be. You can state that you favor the current legalities and that's fine, but simply spouting what the current legalities are will not address the question.