I don't think Howard and Richard had any issues with each other until sometime between 79-80, when they made the daytime version a 300 point game. The E! THS said that Richard was vacationing in Hawaii and threatened to stay there for good unless he got a higher salary. Goodson was ready to let him go, but ultimately they gave in to Richard's demands.
Richard was apparently considered to guest on Password Plus, but with Howard producing the show, and the tensions building up, Howard didn't want to deal with Richard more than necessary. Based on what I saw from Password All Stars, Richard was a very good player and took the game seriously, and still found plenty of opportunities to be funny.
I think Richard was increasingly upset about not having the time he had during the 200 point era, and it didn't improve things when they made Feud a 400 point game. I've said this before, but during the last 2 years of Feud, Richard appears to be hosting the show in his sleep.
I don't think Richard guest starred on any other Goodson Todman game show after 78.
His ego had obviously shrunk when he was asked to come back in 94. His only conditions for returning was that he wanted to get rid of Bullseye and allow more time for Fast Money. They compromised by making the Bullseye game shorter and calling it the "Bankroll" round. This allowed Richard more time to chat with the families and do a brief opening monologue as he did in the early days of Feud.