From https://metaculus.com/questions/16168/dianne-feinstein-resignation/

Born in 1933, Dianne Feinstein has been serving as a US Senator since 1992.

Despite announcing her intention not to seek re-election in 2024, recent health concerns and increasing public pressure have fueled speculation about her potential resignation. At the age of 89, Feinstein has experienced extended medical absences and reportedly exhibited signs of senility, which has raised concerns about her ability to fulfill her duties in the Senate.

As many votes in the current Senate rely on a single Senator's decision, her absence has had significant implications on proceedings, such as the confirmations of federal judges.

In the event of her resignation, the Governor of California would appoint a temporary replacement until the 2024 election determines a full-term successor.