In most states in the United States, if someone dies without a will and without anyone ascertainable in the line of intestate succession, the assets of the decedent escheat to the state.

So, if the person lived in California when they passed, California would own the intellectual property associated with the voice. Why or whether the State of California would ever enforce or even seek to perfect those rights is a different matter.

I don't think anyone would care enough to sue or otherwise make a ruckus, so they'd probably get away with it.