I ran a half marathon on sand with no training, find a pace you're comfortable with and stick to it. Knees were fine, delayed onset muscle soreness the next day was extreme but passed. (had I not had to turn back because of a river mouth I would have gone further)
Ok, I took the whole "your body is likely to get damaged forever" thing as "can not and should not run".
And also, healthy non trained individual wont run half marathon. May walk majority of it, but wont be able to actually run that distance.