In this grand divorce where the west coast states separate from the rest of the US, who gets custody of the dollar? You surely don't think the federal government will continue to manage the banking system and create money for alimony, do you? That isn't how divorce works.

I'm pretty sure that the separatists would find themselves under economic sanctions faster than Putin did. Their (government and perhaps even the citizen's) funds would be captured at the Federal Reserve level within hours and the states involved would be forced to create their own currency with no support from the rest of the country.

Also, even the states in question are anything except a unified front. The urban centers carry a vast majority of votes, but the productive land area that those centers largely depend upon for critical supply chains is very Republican/libertarian. I'm betting they are also "home" to most of the rank and file National Guard troops.

You might be better off asking Canada if it would like some additional population and productive land area. You'd have to accept that pesky single payer healthcare and probably some gun laws, but it just might take you in if you plead very politely. It would like to be able to trade its dollars for ours on such a grand scale.