This is basically my hypothesis too, but with an added twist. I think when one of them dies, they switch bodies too. I know it's a stretch but earlier in the story, someone was talking about how awesome Youngwon was back before everything went to shit and what they said for Hohyun almost uncannily well. That said, the one person who seemed to know Hohyun from one of her classes, and whom he recognized as well, didn't seem to think his personality was of, and Youngwon's could be explained by the multiple extra lives he has had forced upon him.
My main source for this theory is the word"switch" in the title. That said though, it could refer to Hohyun's death being the"switch" that gets flipped to trigger a reset.
Sad you can tell, I'm not only WAY too into this story, I've thought about it way more than is normal let alone necessary. I'm one theory of from going full PhD thesis on this fucker lol.
*As you can tell…
*I'm one theory away from…
SPOILER (from the novel)
To summarize things up, actually yeah most of it it's true. If they don't want to get stuck in time loop, hohyun must stay alive
I think his repeating life and death would only stop if Hohyun lived. Like when that kid said something about a game and he got mad and beat him up.. i think he got triggered because he's in the same aweful situation.