Democrats always replace someone with someone else even more extreme.
Whoever replaces Feinstein will make us wish Feinstein were still in office.
Job description for the average US Senator:
1). Mouth the party line and vote as the party leadership directs.
2). Operate a pay to play scam. In return for campaign money, insider trading tips, private financial deals, speaking fees, book deals, and high paying board seats and consulting gigs in retirement the Senator will insert special provisions benefiting patrons into bills numbering thousands of pages that no one reads.
3). Enjoy government paid junkets around the world, vacations on billionaire private islands, rubbing shoulders with celebrities, great sex, and lobbyist paid dining at the most expensive restaurants.
Even if Oprah was a California resident why would she want a job that is far below her social status, much less one that cannot enhance her lifestyle? Now Meghan Markle would probably jump at the chance to play the placeholder role.