[RobW]

Crippling hits are a great way to help an underdog overcome a more organised and clever foe through sheer luck.

So I would say, if you want the PCs to live longer, don't use crippling hits.

This thread reminds me, when we were first getting our new group going, I gave the PC party a "luck" item (inspired by GURPS) that let them re-roll once per session. Just to avoid killing their characters and their interest, and to let them explore the game a little without such deadly consequence. They never used it that I recall, conservative bunch always kept it in reserve.