One thing that is certain from what I've read is that Louis Edmonds was definitely going to leave in 1971 - and apparently the plan was to kill off Roger in the manner that is described in Sam Hall's TV Guide projection of what happened to the characters after DS went off. Some of what SH wrote was indeed planned for the show had it continued.
I did not know that Louis Edmonds was planning on leaving DS in 1971. If I can recall Sam Hall's TV Guide projection, Angelique was going to be involved in Roger Collins' "departure" from Collinwood. This would have been a big mistake, imo. Dark Shadows without the proud and pompous Roger Collins would have been like The Honeymooners without the affable and zany Ed Norton!
In addition, Sam Hall wrote that Quentin was searching for a man named Count Petofi, who might be able to finally free Quentin from the werewolf's curse. Yet, in the way that Mr. Hall wrote this part of the projection, it seemed as if Quentin was learning of Count Petofi for the first time. Clearly, Quentin was well aware of the notorious Count Petofi from Quentin's own extensive dealings with the evil count in 1897. Maybe I misread that part of Mr. Hall's piece?
Alas, what might have been on Dark Shadows beyond April of 1971. Somehow, after Barnabas returned to the Old House after hearing Roger Collins' speech at the opening of the Collinsport Historical Society in town, I suspect that Barnabas would have been quite shocked to see Angelique waiting for him there in the Old House drawing room, sipping a sherry with a devilish gleam in her eye.
PS It was great to read that Maggie and Joe, two of Dark Shadows' most decent and well-liked characters, were eventually reunited and were married, living happily ever after (which was extremely rare on DS!).