There are a lot of ways for things to take a more sombre turn w/o having to resort to death(s).
Not saying any of them will happen but examples:
- Fired. Candidates; Bella, Cathy, Jade (having sex with a student (MC) would be grounds - could trigger peops who've been laid off?) Not counting Burke as people will be happy rather than depressed with that event.
- Expelled. Candidates; any of the student LIs plus Derek.
- Mental breakdown. Candidates; all except maybe Josy and Cathy
- Rehab/arrested. Candidates; The HoTs/DIKs/Jocks
- Disabled/loses a limb. Candidates; any, but Derek would be most likely
No need for deaths or fires.
Fired: No, it's not really dramatic and all the above mentioned are very much safe - they are very influential in B&R - except Bella.
Expelled: Derek or even MC - but just for a cheap, one update, storyline.
Mental breakdown: I don't know why you think Cathy and Josy are safe? Cathy is in the middle age crisis, Josy already was torn apart with everything around her. But I don't know if that could create enough drama.
Rehab/arrest: Pretty much everyone. Maybe, again, Derek or MC as part of Hell Week gone awry. After all, Jacob had the very same experience.
Disabled/loses a limb: Yes, I would even add prolonged coma. Derek - again - as a possible candidate, but also Neil (dad)
Can it get darker? Rape - off the screen, of course? Kidnapping? That could be related, later on, with mental breakdown etc.
Murder is "nope", if we believe DPC, but how dark - and what he would consider "dark" - the game could get?