So what happened to the girls?

Eight years after the movie was filmed and 13 years after the novel, Yvonne Rousseau published a book called Murders at Hanging Rock, which she explains some of her theories as to what could have happened to the girls:

1. The events took place in a parallel universe to our own. The discrepancies in the date of events, for example, could be explained by a slightly different calendar being used in the parallel world. There is a possibility that the girls had the ability to at least partially levitate their bodies, explaining why Irma was found with her feet undamaged four days after she disappeared.

2. The girls entered some other dimensional state of reality while they were on Hanging Rock. The fact that the people's watches stopped is used to support this hypothesis. Variations could include that the girls actually traveled forwards or backwards in time, or that they may have been involved in time travel, dimensional travel, and travel into/from a parallel universe.

3.The girls became involved in a UFO abduction event. Irma's amnesia and the strange cloud are both used to support this hypothesis.

4. The events could also have involved some form of supernatural activity.

And my personal favorite:

5. What we are dealing with her are some very gruesome murders. According to this hypothesis Mike and Albert worked together to capture the girls and Greta McCraw. According to this hypothesis, Albert and Mike were drinking champagne when they spotted the girls. Mike and Albert confront the girls, Mike holding a knife to Irma's throat. Edith runs away while Miranda and Maion freeze. While Edith is running away she spots Miss McCraw. Albert catches Edith and knocks her out with a rock. Albert comes up behind Miss McCraw and also knocks her out with a rock. The three girls and the adult are bounded and gagged and placed into a cave.
Edith wakes up and wanders off, effecting her escape. Mike and Albert return to the college at night, but go back out the next morning where they rape and kill Marion and Miss McCraw, stuffing their bodies down a hole in the rock structure. They then take Miranda and Irma back to become their own personal slaves. This doesn't work out, however, so the girls are drugged and dropped off in the bush. Later the girls are again collected and Mike and Albert head back to the rock. Albert then rapes and kills Miranda. Mike is left with Irma, and Albert leaves. Irma manages to get a rock and hits Mike with it, gashing his forehead. He falls and knocks his head against a boulder. She crawls away and is later found. Fortunately for the murderers Irma has been hit enough times with rocks and suffered enough that she now has amnesia and can't remember the events.

Unfortunately, several explanations are presented in such an incredibly boring manner that it becomes a pain to try and force your way through those sections. Only section 4 was readable, but never dealt with this problem: how could two teen-age boys manage, in reality, to subdue three girls and a grown adult, pull off all four murders, and never ever be caught. It isn't like the two boys were accomplished criminals; probably neither had any experience with anything along those lines.