In the far-fetched scenario that the hypothetical proposition in question even makes it on the ballot, I would be absolutely astonished if it doesn't go down in a historic landslide.
Brexit was supposed to be hypothetical, and when it wasn't (Thanks Cameron), it was supposed to go up in smoke...neither happened.
Enough trump failures, enough far-right agenda advancing at the cost of Californian values, enough polarization in general, enough people not caring jack about the consequences and this could very well gain traction AND pass.
Highly improbable [as in, another attempt by SNP to take Scotland out of the UK is more likely], but not impossible.
Your post causes me to think that there may be another variable that needs to come into play. Even if Dem voters in CA want independence, I strongly doubt that the national Dems could support it in any way. That would extend to most elected Dems in CA, particularly in Congress. I think that for this to gain traction, there would need to be a CA independence party in the mold of the SNP. They would need to start working the top-two primary system to get elected officials who were formally free of the national Dems, but could work with them as SNP does with Labor.
This CAIP might concentrate on state government. Given the supermajorities for the Dems in Sacramento, there wouldn't be too much fear of this giving the Pubs a chamber. If CAIP tactically concentrates on seats with relatively small numbers of Pub votes, they can use the top-two to make Nov races a head-to-head with the Dems. In Pub areas they can try to beat the Dem in the primary and make it Pub-CAIP in Nov; the worst that would happen is a Pub-Pub ballot in a district that already was likely Pub.
