Here's something I was thinking about and I hope you can all do me a favor so we can get a consensus of different personalities and how they would react.
Please put yourself in the fiance's shoes for a minute. It's the 1970's, you're in your 20's, you're driving and your non-live-in significant other is in the passenger seat. You get into an argument (use your own imagination for what the argument would be about), and your significant other storms out of the car. There are no cell phones, facebook, etc.
What would you do?
I think I would let him go and I'd go home, or somewhere to cool off... and let him cool off as well. I don't think I would go straight to his parents house, since I wouldn't think anything was wrong other than an argument.
If I felt I was in the wrong, I might call him a few hours later to apologize. If I got no answer, I might go to his house to apologize, or I might think he didn't want to talk to me yet and give it more time. I wouldn't get his parents involved in our business.
If I felt HE was in the wrong, I probably would wait at least a day, maybe even longer, thinking he should call me to apologize. If I got a call from his family saying he never came home, however, I would probably get worried and start trying to find him.
I wouldn't think he was missing otherwise.
If I did hear he was missing from his family, even if THEY didn't want publicity, I would - I was the last person to see him, and assuming I wasn't guilty of anything, I would want anyone who saw him walking alone to come forward... and I would feel guilty that the argument happened, would want him to know I loved him, etc... I'd be posting signs and contacting the newspaper, etc.
That's me... maybe other people would have different reactions.