even if the us were to begin a process of balkanization, the irs is how the federal government extracts value from its citizens, so i imagine it'll be the last to go. in many empires, one of the last bodies to stick around has been the tax collecting arm, long after any actually useful offices are closed.

even the ottoman empire, whos dissolution was pretty fast, took about ten years from what is considered the start of its dissolution. the mongol empire, considered to have begun collapsing after kublai khan's death, stuck around for several decades, and that was also considered relatively quick