These comments are from interview transcripts you posted awhile back Nancy. I think they offer some interesting insights into that question. I think Jonathan Frid would have unquestionably been the next horror film icon along the lines of Karloff, Lugosi, Price, Cushing etc.. Perhaps I will post the question on Jonathan Frid's website to hear what he has to say about it today...
Jonathan Frid from a November 1971 TV By Day interview: Ive been offered roles, but I wont do Barnabas or anything remotely related to him. No vampires, no monsters, no necrophiliacs!
From the same interview: As for movies, well, to be very honest, its a very different
thing from television or the stage. There is so much waiting around, so much boredom. You have to stand there while they arrange lights and things, and it takes forever.
John Karlen from 1977 ShadowCon interview: Between you and me, I feel he (Jonathan Frid) made a great mistake by not doing the second movie, because he was right on the verge of becoming one of the greatest horror film characters in this country. That was totally his prerogative. I think he had it at the moment with that kind of thing as an actor, but to me, if he would have continued on with it, he could have branched out into just about anything. It just didn't work out that way.