as for doctor b's duelling prophesies, if you can only slay the god by having the evil sorceror take over your body permanently. both prophesies can in fact be true.
I say do not allow them to find out what it does, you say the sorceror had allmost god like power, surely his last ditch effort to keep himself alive could shield itself from mortal magic.
I would have the ring begin to cast little spells like bulls strength, cat's grace, invisibility when a hide check sucks ect on it's wearer when it's needed, have it help them alot and seem to be a great buddy until they trust it. then have it reveal it's sentience to the wearer. have it offer him heplful advice in a situation where he really needs it to stay alive (you can easily arrange such a situation), then when they need it to kill the god have it ask the wearer to let it do what must be done to destroy it's enemy, never relly revealing that this will mean the destruction of the character.
pick a player you trust and have his character be the chosen target of the ring and when he puts it on, he can't get it off, have a prohpesy say that the ring can only be used by a direct decendant of the sorceror, and make his character such a person. do not allow even a wish or miracle to remove the ring. try giving the characters things that they must do immediately to further the quest and keep them occupied with other matters having the ring do nothing unless it is nessisary to keep it's chosen host alive and doing no more then that. do not let it have a visible effect on the character ever. i would give no indication of it's true power. when it kills the character make the player's new character the target of another prophesy detailing how to kill the newly risen sorceror as payback for dooming his previous character.
