By not stepping down he avoided the 2018 election and kicked the can to 2020 for whoever replaced him
Arizona does have a uhh fun? provision though?
> For a vacancy in the office of representative in Congress that occurs simultaneously with at least one hundred additional vacancies in the office of representative in Congress as prescribed by 2 United States Code section 8, a special general election to fill the vacancy in this state shall be held not more than forty-nine days after the declaration of the vacancy
(unless there's a general election within 75 days)
But that's effectively a "What if actually the whole US Congress is yeeted?" clause