Having played a healer in many online games, I've discovered that triage (what you've described above) quickly becomes second nature, to the point where if someone performs the wrong response to a threat, I will literally say aloud, "go die then" because I have more important people to take care of. I consider it a signature of the best healers that they will abort a spell on someone who needs it to instead cast it on someone who is more important.

A true trolley problem would have to be contrived by a murderous, insane villain ala Saw; the uncertainty remains in any real world scenario that I've come across

Though perhaps organ transplants can serve as a stand-in. Tons of otherwise healthy people just need one organ to live out a good life, and tons of people who are somewhat negative utility have nice, juicy organs. We'll know we're on our way to fixing the trolley problem when organ donation is mandatory, and can be a punishment handed down similar to the death penalty for those who harm society.