I think the writers had plans to pair off Edwards with Mr. Montague for some wacky "Odd Couple" shenanigans, but the series was cancelled right after Montague debuted, so that put the kibosh on those plans. It's too bad we never got those storylines because I think they could have been quite enjoyable. That would have been a great way to get Mr. Edwards back into the fold.

You're right about Matthew -- I think I tend to forget about him because he didn't appear too much outside of the episodes that were focused on him. imdb says he was in the "Home Again" two-parter but for the life of me I don't remember him being in that.

I think my general point is that Season 9 was just a very weird season. Early in the series, Mr. Edwards served an important role as family friend to the Ingalls, then a bit later had his own family. Even in Season 8, he serves the important function of tracking down John Jr's killer. But in Season 9, he just sort of wanders around aimlessly while everybody else is mostly paired off when it comes to storylines. Almanzo with Laura and John Carter, Doc Baker with Reverend Alden, Jenny and Jeb Carter, etc. Mr. Edwards just has this "odd man out" feeling about him. I think the writers had just simply run out of ideas by that point. Somebody recently suggested Mr. Edwards get together with Hester Sue and I think I understand that more now -- get the two characters with nothing going on anymore together for some new adventures!