To secede, you need access to at least one sea water port.

The cities, including the port cities are going to be really chaotic in a collapse scenario. I don't think the new liberal empire would be able to reliably hold all their ports when their own subjects are killing and looting each other for food. Many quality people will also abandon liberal cities to live in the secession areas which will make the areas more sustainable even without immediate seaport access. Large groups of high quality whites with a purpose know how to get things done and getting access to supplies via the ocean won't be a major concern.