Where have they disappeared to??? Why haven't they come back for Val and Diane??

Very good question

From the Thursday preview on the ITV site, Rodney, Eric and Doug go out drinking out of the village. They'll return on Friday and find out about the accident.

Although surely that suggests that they planned to leave them there all night? How else would they have gotten out?

I missed it, but apparently they referred on Wed to the three of them (Rodney, Eric and Doug) going to the Malt Shovel for a drink after they locked Val and Diane in. So not far and presumably they just planned on leaving them there a few hours at most?