I'd always assumed that Mr. Rushworth got a full Parliamentary divorce, that is an Act of Parliament - he is, after all, extremely rich; and his intention, thwarted by Julia and Henry Crawford, was clearly to settle down and have heirs. He has quite clear grounds for the divorce if he wants to go through with it, nor will Julia oppose the various stages of the divorce - she has no money to do so, and her friends will certainly not help her. Doesn't JA talk about Mr. Rushworth getting a divorce and remarrying in a year or two? I don't have MP to hand.