Barbara Lee is trailing in 3rd, so even if Newsom appointed her, it wouldn't pre-ordain the open seat election. AFAIK Lee is in good health but after Feinstein hung on for way too long, Lee's age is disqualifying.
If and when he appoints someone else, I doubt that Senator can defeat Schiff or Porter.
The reason is because today's GOP isn't one party or even one coalition. You have traditional conservatives, and then the MAGA Trumpian wing that was borne from the Tea Party wackos. The latter extremists are really a separate gang that is loosely affiliated with the GOP. The problem for the country is that moderates have left the GOP so the balance has shifted towards the extremists, even if they seemingly number in the few. Kevin McCarthy reps a pretty conservative district and he's never been accused of being a moderate Republican, but the Freedumb Caucus treats him like dirt anyway.