Antenna TV currently is re-running third-season episodes of Dennis the Menace. It's funny how little things during the season set up George Wilson's eventual departure (unintentionally, of course). In the episode "The School Play," it's mentioned that George owns property in Ohio. A few weeks later in "Mr. Wilson's Inheritance," he is basically the sole beneficiary of his aunt's estate.
And who can forget the episode that aired the night after Joseph Kearns died, "Mr. Wilson's Uncle," in which many references were made to George's mortality?
Of course, no one could have foreseen what was going to happen. But George's departure, and of course that of Martha's, actually had some basis in merit given that he went "back east" to settle an estate. It's very plausible in the show's canon to see the Wilsons living in Ohio on the property they previously owned after George spent considerable time working out an aunt's estate (it's never said specifically whose estate he was settling or where George and Martha settled after they sold the house to John and Eloise).

That is interesting how things we're set up in an unintentional way. Perhaps the producers looked back on the season and then got the idea for how to write George Wilson's departure from the show.

I've always liked the fact that they chose not to have Gale Gordon play the same Mr. Wilson as Joseph Kearns. Making him his brother was a much better way to go. Although I do feel really bad for Sylvia Field.

I have said it elsewhere, but I truly don't think the show could have handled Joseph Kearns' death any better. That said, it's still sad watching those last Season 3 episodes because you know Martha is on the way out and nothing really could have been done to keep her. I also liked that the show threw in at least a couple references to George and Martha in the fourth season.

I always wondered how odd it must have felt for the cast (especially Jay North) to mention George Wilson being "away on business" as though he'd be back. Although I'm sure they never say he'll be back.

True, I don't think any cast member explicity said George would be returning. It was more implied than anything else by just calling it a trip. I watched the Season 4 pilot yesterday on Antenna TV, and when John told the Mitchells he'd bought the house from George and Martha, it's almost easy to imagine a going away party being thrown as John and Eloise moved in while George and Martha moved out.

Sylvia Fields was unfairly fired from the show. The producers didn't even allow her to do a few guest appearances.

But why would Martha come back and not George? There'd always be that elephant in the room. Granted, I'd have to loved to see Martha and Eloise interact just once, but there'd really be no place for Martha in a guest appearance.