If you have that key item and fall in a hole, like for example trying to go up for Quest/XP/EMN, then you must examine the 'fracture' of the ground. If you have the key item a context windows will pop asking if you wanna 'use it'.
Once you use it you will back to the upper level. The 3 times i did that i poped free of agrro, with just a few seconds to sneak/invis and keep going.
Also, and very important, when you use the key item you Lost it, so in order to be safe you need to re adquire the Ethernal Ice again, just in case you fall on a hole.