Shy,
Good questions, and important ones.
generally, no parts will fail for a 10% overtorque (at least on the helos I have deep knowledge of). Remember, this is a very broken machine you are flying home, and when you land safely, and get down from the shoulders of your passengers who have been carrying you around singing "For he's a jolly good fellow" with true passion, you can write up the over torque! A few seconds on touch down are no sweat, IMHO.
For the rotor rpm on touchdown, most helos suffer those transients on HV engine cuts, and touch down at somewhere around 80 to 85% rpm as part of the certification testing. We have to show the FAA some reasonable data to show that this is not a catsatrophic event, so we know that is ok.
If you ever saw "The High and the Mighty" then you will understand what I am discussing. The old former captain, now a washed up co-pilot, brings the crippled airliner back across the Pacific by vastly over boosting the remaining two engines, knowing he is damaging them, but also knowing that his fuel consumption is now low enough to let their fuel last to shore. He has to smack the young, by-the-book captain to make his point. Sometimes the limits can be "reinterpreted a bit" in a true life and death emergency!
Here is that clip, which illustrates my teaching style, the one I learned from SASless:
http://www.s-92heliport.com/highmighty.wmv