Depends how good they are at it. They might not need to heal anything to keep someone alive. [Momo is 99% sure Yuki is still safely asleep, otherwise he probably wouldn't be having this conversation. Even now that Yuki is aware Momo is a bit messed up, he doesn't tend to show it off in front of him unless he has to.]

That's usually how making an example of someone works. A lot of countries in my world banned the death penalty, but there are still ways to punish something hard enough that nobody else is going to want to try it.