If we are legitimately making this comparison, I would talk to my cheater about the benefits of not cheating, but I would also recognize that his cheating is legitimized, at least to me, because the results would be literally life-saving. Literally that. As for the other students, we would have the "fair is not always equal" talk. I'd also get real. "Do the lives of your family members literally depend on passing this test? No? Then zip it, do your work, learn this stuff, and do your best. If you fail, you can try again. If this kid fails, he's dead. Literally dead. You're privileged enough to not be in that situation, so you don't get a pass from me when it comes to cheating. What you do get, simply by virtue of being in my class and being someone whose success I care about, is a number of chances to try your best and to get as much help from me as you need."