Except that Sal doesn't have a moderate, as she was healed magically to a mild.
Assuming the NHS works at all like the Canadian system, Sal going to the hospital would be like a 13-hour ordeal of waiting, because after the first triage nurse confirmed the wrist wasn't broken, she'd be marked low-priority and given a wonderful seat in the waiting room (single-payer health system is excellent for critical care, but waiting times for non-critical things can be pretty high -- especially given some people use the ER in place of having their own GP...).
(Otherwise, Kenneth could have used the mental stress he took downgrading Sal's moderate to heal away Danny's mild... to make sure he didn't cry about potential scarring..)
Milds are just that: mild. Enough to slow a body down for the rest of that scene and the next... then you're better (think of all the times Harry just needed a hot shower and a moment's rest...)
In terms of Kenneth, if he weren't magically reinforced, he'd be looking at having someone splint his ribs and would be a while recovering. However, having been beaten by Trolls, he's got a pretty decent idea of how durable he is. Plus, his rapid healing is such that he'd probably get better before a doctor looked at his X-Rays... And then, too, there's the small matter of needing to keep his temper as to not accidentally fry many thousands of pounds of medical equipment.