You decide crawling along the ledge slowly is the most prudent choice available.

The remains of the stairs that cling to the wall seem treacherous, but no more so than the other options. You sidle along the wall carefully and do your best not to look down. You have to test each jutting stone before you can commit your full weight to it - there's no recovering if one decides to break loose! But with each cautious step, you inch closer to the other side of the gap. Just a couple of feet away - one of the rocks beneath you begins crumbling loose!

In an attempt to salvage the situation, you reach out to the far ledge to get a more solid handhold. Instead, shifting your weight to the stones so violently makes it crumble away in your grasp - leaving you to plummet back down towards the lower stairs! You hit the stone hard, unable to keep your balance and tumbling even further down.