Since the EoC is coming and Glaiven boots will require 85 defence (which I don't yet have) I'm considering putting them on with the help of a defence potion. When my defence falls below 85, what will happen with the item? Will it be unequipped or lose its stats?
I think the same thing happens with P2P items when you hop to an F2P world, i.e. it not only loses its stats but "vanishes". For example, if you equip an abyssal whip, then hop to a free server and attack something, you will be attacking it unarmed, but the whip will still appear in your equipped items menu.
I dont think youll be able to wear them at all. Like @murgatroid99 said, it depends on your natural stat, not the modified one you will have from drinking a defense potion.