By that, I mean how many plots from season 4 with John and Eloise Wilson would have been equally plausible with George and Martha still around?
I can think of several ... including "Poor Mr. Wilson," "The Little Judge," "Wilson's Little White Lie" and "Dennis and the Homing Pigeons" among others. Some of them definitely would not have worked with George and Martha, including any that centered on John's writing career and especially "Baby Booties."

I believe most would not have worked with George...... It almost looks as if they started to write and create a series around John's earlier life experiences.... Ex: At the end of season 3 I believe, where all of the neighbors thought John was a witch doctor would have never worked with George.... That was a very funny episode and will be plugging that one in tonight....

Anything involving George and Martha showing any affection towards each other. No on the Gypsy episode. My 4 sons could have worked?

I agree the writers took a new Mr. Wilson as an opportunity to create story lines they never could with George.

I believe most would not have worked with George...... It almost looks as if they started to write and create a series around John's earlier life experiences.... Ex: At the end of season 3 I believe, where all of the neighbors thought John was a witch doctor would have never worked with George.... That was a very funny episode and will be plugging that one in tonight....

Agreed. Like I said earlier, I do think a handful would have worked, probably a bit less than half but certainly no more.
I always thought of "Dennis and the Witch Doctor" as the de facto Season 4 pilot, getting Season 3 viewers ready for what Season 4 would be like. Although John was living in what at the time was still George and Martha's house, George was not mentioned at all, Martha was gone and John acted like he was intending to stay for a while.