> I've characterized the Queen's powers as "reserve powers" inasmuch as, if everything goes wrong and Parliament dies from a meteor strike, the government still legally operate provided there is a monarch (even if you have to reach deep into the line of succession to find that person).

Ignoring that the Queen and much of her staff would likely be dead, where exactly do you think Governments come from? Parliament would just reform and be recognized de facto until the laws were either reconstructed or replaced. Sometimes words have no meaning, and the queen has no practical power to do any of this, so it's basically irrelevant in my view.