That's kind of a silly question. Basically any reasonably-defined geographical and cultural region with more than about 10 million residents can survive as a se

That's kind of a silly question. Basically any reasonably-defined geographical and cultural region with more than about 10 million residents can survive as a separate country. California certainly qualifies. The question with all separatist movements (Scottish, Quebecois, Catalan, etc) is whether the costs of the act of separating are going to be worth the immense hassle. Britain is trying to go through a something similar today and they're finding that the nitty-gritty of it seem to be more challenging and complex than the simple campaign promises. Belgium may actually be, inadvertently, the model for how modern nation states do separation. Continuously devolve more and more power to local governments until the central government sort of atrophies and it hardly matters whether you're in or out.