First off, I think the progression should begin with whether or not Sanny Fanny wants to dissolve from the State of California, as city government's next step up the pecking order is State government, and as I consistently preach, one of the purest tenets of the glorious Struggle for Southern Independence was and IS the staunch support of States' rights. Old lady Jefferson's boy wrote a right smart little treatise that addressed them. Called it the U.S. Constitution or some such. People oughta look into it sometime.
Supposing SF wished to do so, and by whatever means was able to in fact accomplish this, IMO the ball runs to the feds' court at that time.
I personally would not support an individual city's attempt to become sovereign. I say this because I cannot fathom a city being able to become self-sufficient economically. They could not hope to provide the infrastructure needed, plus the military force required, plus all the functions of a free and independent government all by themselves. Demographics notwithstanding...
Were the question one of a solitary State wishing to do so, then yes, by all means, I'm right there with them. Be it South Carolina, Massachusetts (who tried it themselves, how ironic), California, Texas, or Hawaii. With the following two caveats: 1 - it must be by the will of the people. 2 - it must be irrevocable, or at the very least irrevocable for a minimum period of 100 years.
Naturally, should a group of geographical neighbor States, each of like mind and with consent of their governed inhabitants, wish to, oh I dunno, maybe LEAVE A VOLUNTARY UNION AS THE CONSTITUTION AND ITS AUTHOR ADVOCATED WAS THEIR SOVEREIGN RIGHT FROM DAY FRIGGIN ONE after making reparations to the fed for the unremovable infrastructures located therein, in peaceful harmony as a friendly neighbor State, to coexist as an ally of said mother country yet independent from crippling tariffs, unholy nondistribution of national resources, skewed practices of governmental representation, and aggregious breach of contract/Constitution, I'd be right likely to jump all over that like stink on shit. Pick me up a squirrel rifle if need be to support it in fact. What time is the rally scheduled for Monday, I'll be there. But at the level of each municipal government...no. Answer to your State first, it's not a federal issue.
"It's not a federal issue"...God, how much better off we'd ALL be if we heard THAT a little more often. Providing your healthcare, raising your children, seeing to your retirement income...NONE of them should be a federal issue. Unless you're a Demonrat, then EVERYTHING should be handed to you on a platter by the nanny state government. "Give me a job, then take 85% of my salary and just provide me with what I need to live. Tell me where I can smoke, what restaurant to eat in (trans-fat policies), all that. Because I'm an idiot incapable of taking care of myself...I want Uncle Sam to do it." Disgusting.
See, this is why y'all oughtn't to ask me nothin'...
Deo vindice, my brothers. And hopefully that right soon.