for the which dies first puzzle.

First, a simple continuity error on Jane's part, which her publishers failed to spot. (Nor have numerous critics, and David Shapard does not mention this point in his annotations. So Stephanie and I and anyone else who always wondered about the discrepancy may be insufferably smug about our perspicacity).

Second, either Darcy or Wickham is lying and if so it has to be Wickham. Darcy would have no possible motive for it, as the exact date of their respective fathers' deaths is irrelevant to the points he is making about Wickham's character. But by the same logic it's not really relevant to Wickham's attack on Darcy's character either, and Wickham does not usually lie about matters which are publicly known - he does not, for example, try to say Darcy is a bad landlord, he just imputes a questionable motive for his being a good one. The only reason I can think of is that his language in telling his story is remarkably like that of a sentimental novel with himself as the wronged hero, so he has written in an affecting deathbed scene that didn't happen.

Third, either Darcy or Wickham's memory is at fault. But that seems unlikely for such important events as the deaths of, in Darcy's case, his father and a long-term and diligent employee of his estate and in Wickham's, his father and his godfather and patron.

Fourth, the same scenario you suggest, Line. Mr Darcy senior, grieved to hear from the physician he summoned to attend his faithful steward that nothing can be done for Mr Wickham senior and he will die in months if not weeks, goes to see him and assure him his son's future will be secured. He is so upset he ignores the symptoms of an impending heart attack which strikes him down that night.