Those are some great points. I admittedly knew that there were likely areas that I overlooked as I thought about what a secession might look like. I have rebuttals to a few of the points.
When I looked up where California gets its power from, I found that a portion of it comes from Oregon and Washington, so if the three states left as a unit as opposed to just California, that could help with that problem.
From what I understand from https://en.wikipedia.org/wiki/Water_in_California
it isn’t that we are getting most of our water from out of state as much as it is moving around the water we do have access to.
Banking was an interesting area of research after your point. It might turn out to be significant that California recently passed a law allowing municipalities to create public banks that are not tied to the federal government. https://www.publicbankinginstitute.org/2020/01/16/bloomberg-law-california-breathes-new-life-into-the-public-banking-movement/
If these states were about to make a solid push towards secession, they would want to pull cash into these banks before making any public announcements.
Also, there are always foreign banks and foreign investors, who are already heavily tied to California’s businesses and have a lot of reasons to continue to support those businesses, even if these states were pulling away from the United States.
But, all of your points assume that the Federal Government would try to damage this new Pact as much as possible. Which is one possibility if it goes to civil war. However, what if it was peaceable, with negotiations and trade agreements. Instead of freezing all cash, giving us a chance to move loans and funds to banks not tied to the union, that kind of thing. If the separation was made with diplomacy instead of war, many of your issues would likely be in the terms of the split, much like agricultural trading would be in it for the nation left behind.
But still, good points. Separation is never perfect, but I think most of the issues could be worked out in time, through new arrangements, treaties or other negotiations.