I heard about this today on the radio, but I didn't realize his tumor was this bad. Terrible news.
And the tragic irony here is that his mother (who's around 105, if I recall correctly) is very likely to see her son die, which is always one of the worst things a mother can experience.
That said, if he dies or retires, particularly before the midterms, how would he be succeeded in the Senate? Would there be a special election or would the governor appoint someone to take his place before the next regular elections?
Governor Ducey appoints a Republican to fill the seat and there would be a special election on November 6, 2018 to carry out the remainder of the term until January 3, 2023.