I think "dom" is correct. Tom Happer didn't appear in a lot of episodes -- and didn't appear in winter 1971 (1841 PT) and spring 1971 (NODS)... BUT, if the franchise had continued, he was probably going to have a large role. He was considered a regular (!) and I think a bigger role would have been developed for him on the TV series.
It's believed he was brought in for his heart throb appeal in David Henesy's absence, and I do get that you're speculating, but I don't understand what you mean by being considered a regular.
Through the winter of 1971, the TV series tightened up... by that I mean no elements of a future storyline were introduced, so Mr. Happer's phone didn't ring.
Is that more speculation? PLEASE be clear about it if that's what you're doing. The forums have a lot of readers and I'm sure you wouldn't want to be misleading.
The contracted players who wanted to stay moved on to NODS.... but some of the newer players got "bumped" -- Happer & Cody. I think Vestoff bumped herself. She was going to be in NODS, but Diana Millay replaced her.
Vestoff didn't appear in the movie because she was already appearing on stage in 1776.
Millay was set to return to the TV show, but did the movie instead. You can take all of this with a grain of salt, dear reader, like you should do with any official version of the same "facts!"
Was Millay set to return to the show? I hadn't heard that. And actually, while I understand your point that official facts can sometimes be questionable, what's considered to be an official fact on the forums is what's been publicly spoken or written by any of the DS personnel or published in a reputable source; the rest is considered speculation and/or gossip. FYI for everyone (since we have lots of newbies to the boards), if the latter violates a person's privacy, is libelous, or it's being presented as a fact when there's no official information to support it, it may get removed by one of the moderators.