Finally finished translating the sex scenes; just finishing play testing for spelling errors or overruns so should be able to throw it up here this weekend sometime. Gonna fix up that walkthough and put it in English while I'm at it.
As for the NPCs, the males die straight up if you don't find them in time, the females become zombies (with the exeption of Yamano who stays normal for all 8 days). The females only get into tied/rape situations if you find them, bring them to the cave, then they get abducted from the cave during a zombie raid (putting the scarecrow out front summons a raid at 100% chance, and drugging the girls to sleep with a blue fruit causes them to be abducted at a 100% rate, otherwise you're playing the odds). After abduction the girls return to where they were first found; if they would be normal (based on the day of play) they are now in a tied/rape setup; if they would be zombies (again, based on the day of play) they are now zombies. Yamano (the tomboy) normally never becomes a zombie but will on day 7 if abducted (or the day after you rape her). Also, Ishii and Furukawa (the lesbians) don't have a tied/rape event; if Furukawa is abducted they both immediatly become zombies where Furukawa (the glasses girl) spawns (unless Ishii isn't in the cave, in which case she becomes a zombie when you tell her Furukawa's fate). I don't think any NPCs simply disapear, but maybe it's a bug or something.