This quote from Ruth's father to Martin Bright:
"I’ve made the final decision that I don’t wish to participate in this particular project. I know that you will do a good job and your part is going to be very professional, like you have always been in the past, but it’s a complicated one and I’ve made the final decision. You can probably tell from my voice that it’s quite an emotional one."
I think this is a very big clue - his daughter is missing, he apparently has no idea where she is, or what happened, but instead uses the phrase "it's a complicated one".
There is obviously something much bigger than the surface story to say it's complicated - I do believe, JMO, that the family know exactly what happened (that she ran of and started a new life) and either have said nothing to avoid media and public scrutiny or because Ruth has told them not to.
I don't understand why the police/family wouldn't just issue a statement saying:
"It has now come to our attention that Ruth is alive and well, and has chosen not to be a part of our family. She does not wish to speak to the media and nor do we. We ask you to respect our privacy and hers, at this time."
Surely - even if there was an initial flurry of interest at this statement - the long term effect would be that the pressure, the scrutiny, the mystery, would be gone? Going missing isn't a crime. I don't think?
'It's a complicated one' could mean all sorts of things. It could be that his wife, who isn't Ruth's mother, doesn't want him getting swept up in it all again. It could be that he has compartmentalised his pain and his own mental health can't stand the strain of opening up that box. Or it could be nefarious, ie he has something to hide.
I don't feel convinced that it's complicated because he knows she is actually alive. To me, that would make it simple: she's alive. You don't need to do a documentary. End of.
Why would they want the shadow of murder/suicide hanging over them?
For Ruth's sake?
IMO that seems unlikely.
Also, even if Ruth did run away, I don't feel convinced that she would subsequently tell her family that she's alive. I think that's something you take to your grave. To go to all that effort to run away, to ride out the police investigation, the tv appeals a year on, unless it was a massive cry for attention (which I don't believe) then why then turn around and tell them? She must hate them, to do this to them. We don't know to what extent this was deserved, but the facts we do know make it clear there was a LOT of difficult history. I feel like if at any point she reappeared and said 'I'm alive' then the family would want that to be made public, in order to clear their names.
Having said all that, I personally do not believe that Ruth is alive. I think that she came to harm on that evening. And i do not think she killed herself. There are too many unanswered questions and too many avenues that were unexplored by the police at the time.
But I would really love to be wrong.