Sierra did do Johnny Castaway. My memory is that it was Jeff Tunnel’s idea (at Dynamix, one of our subsidiarys).
It never gets the credit, but Johnny Castaway was HUGE for us. I bet at least a million copies were distributed over the years. We should have upgraded it and re-released it, but never did. Too bad — it was a very cool product.
As to Mystery House’s public domain status. My brother, John, did formally announce that the game was public domain — which is an ambiguous statement. Was he making the trademark public domain, or was he making the code public domain? I don’t know, and I doubt he knew at the time.
Doesn’t trademark law have a 17 year timeclock? Does anyone know? Or, is it 75 years? I don’t remember. If it is 17 years, Mystery House is public domain anyhow.
Realistically, this is a product that Sierra abandoned, long before most the people reading this post were born. I doubt they have retained any rights to the game — but, I’m not a lawyer, so I must say that I can’t answer your question.