Feinstein resigning would be great but wouldn’t be certain the Newsom would nominate Schiff even as temp replacement.
22 years of House seniority is a lot to cough up. He starts at the bottom in the Senate, coming in ahead of the rest of his class by virtue of that House service, but that's it. The only members of the Senate with comparable House tenures are Schumer (18 years) and Cardin (20). Schiff would end up much more Cardin than Schumer, as Schumer first got elected to the House in his twenties.
His gripe appears to be that McCarthy will boot him from the ranking member chair on Intelligence, by denying him the committee assignment. He's probably better off swallowing his pride and biding his time. He can quickly slide up the food chain to posts like the chair/ranking member of Armed Services, Rules and what not on the way to Appropriations and Ways and Means, if he stays put.
It's not like the media will stop talking to him. He'll be the Democratic face of the chamber with Pelosi gone, since he's such a good interview.
The only way it makes sense is if he thinks he can be the presidential nominee in 2028, in which case I would still tell him to launch the bid from the House. Sure, a mere representative hasn't managed that in ages, but we just had a 'no experience' president. The rules are a little different now.