This is just too unrealistic. I mean, some people actually suffer from conditions where they have a really hard time healing wounds, like lack of plackettes. And some people bruse extremely easily. But if you were unable to heal at all, you would be long gone. Kids get scratches all the time, and even one scratch would lead to an infection that would overwhelm you immune system.
The problem with one time purchases is that you might be investing time in an app that later will go out of business. Keeping an app up to date requires real constant work, before you even think of adding features and fixing bugs. People got used to paying 2 bucks for an app and keep it forever. That’s completely unsustainable.