If the skeletal king doesn't pick the ring up beforehand, it should be possible to lure him out, take it, outrun him and leave. Personally, I always kill him, and with Lightning Ball in your repertoire, it shouldn't be too hard for you to do the same. Anyway, whatever the choice, set Coward tactics and watch out for confusion, the most frequent cause of YASD in this level.
Yes, she always leaves a corpse, although you usually won't get the full +6 if Le is higher than 20. That's why I suggested exploiting starvation. You can also bless it for a chance of extra PP and +1 Mana.Other side question: does the Oracle always leave corpse? If so, +6 Le sounds tempting (I have means of death ray resistance, and some decent missiles). I think I have killed her in one of my games, but I cannot remember exactly.