I like reading your premises, but I think we read this letter differently in a couple of points.

First off, I delight in the phrase "with whom it had always pleased him to be at variance." It is so clearly saying, 'it is not YOUR fault that the two of you did not get along! Dad was just like that...' This is an especially humourous kowtowing as I suspect (somewhat from later information, 'tis true) that Mr. Bennett razzed a bad-tempered relation into setting whatever-the-disagreement-between-them-was in concrete!

But, really, I think you misunderstand the way 'hereafter' used to be used. It did not used to be applied to 'the hereafter' almost exclusively, the way it is today. It was a pompous way of saying 'after this,' too. So, when we see it without 'the' in front of it, it usually means 'later on.'