Both kidneys or just one? I know a rider that landed on the end of his handlebar and he lost a kidney as a result. No operation or anything and it was I think absorbed by the body when the one kidney stopped functioning from the damage. Doc told him that was a fluke accident and told him no reason to stop riding. Hope it works out well for you. Considering such a helmet myself for next time I replace one because i am riding harder and these last three weeks I've crashed four times. Nothing particularly serious but my chin did brush against something in one crash. No marks but the skin burned for about an hour. Weird. But it demonstrates how little control you have when you down unexpectedly.
I did not take a hit to my kidneys , but my protein count way up at top end of chart. Dr thinks it is unrelated and got lucky to find out by accident..