First: Up to you, really. You decide how important that NPC is, if they serve or could serve some purpose in the story, allow them a chance to stay alive, otherwise, don't bother, if it's just extra bookkeeping.
Second: I am guessing there is a limit to the AGI and INT stat (+5 maybe?), and these skills give you the chance to boost your initiative or your spell casting checks even further. I don't know how realistic that is ingame though.