From time to time, one of the All can be divided from the One and All mind. This is a traumatic event, and it is rare that the severed member of the All survives, let alone becomes a solitary One. But from time to time, it can occur. Seeking succor from the desperate silence in its mind, the One Beneath The Waves has sunken himself beneath the oceans of Shamash II, and there it lies, seeking fruitlessly to soothe its injuries.
A possible answer to what happens to spells when a mage dies. If the spell is strong enough, say and enchantment or other permenant effect, part of the mages spirit may become lodged in the magic. It may be a way for items to gain some kind of intelligence, but a mage who has knowledge of this fact would be very hesitant about enchanting anyone or thing. He might have other plans for his afterlife than counting the change in your bag of holding.
Preists, I think, would have this sort of thing covered.