What happens if a character's stats are lowered, reducing the number of spells they can prepare?
Say a level 1 cleric has a Wisdom score of 18. According to the Spellcasting feature , they can prepare 5 spells (Wisdom modifier of 4 + 1 level of cleric). Now say the cleric obtains an ioun stone of insight and attunes it. They now have a Wisdom modifier of 5, so they can prepare 6 spells and do so.
What happens if they then unattune to the ioun stone?
The rules say they can only prepare 5 spells again, but they don't indicate that the character automatically loses one prepared spell from what I can see.