Still, when I saw the headline that he had died, I had to make sure he was a sitting Senator, not some former Senator.

Regarding the replacement process, as characterized by KE, that is interesting to me, in particular because it is a typical appointment process in Spanish speaking countries. For instance, for Supreme Court justices and other state institutions, often the nominating actor submits three names (a terna) and the appointing actor must choose one of them. I think there are similar provisions for some state commissions in the US. But I was not aware of any such provision for replacing Senators.

Of course, there should be a special election.