I, too, had this exact same problem: Failing the 3rd question can "turn off" the riddles before the bridge has been fixed, thus stopping the Unseeing Eye quest cold.
Your Options:
- If at first you don't succeed, give up. (Hey, it's an option!)
- Reload. Your Auto-Save should be at the bottom of the stairs, but since you say your last Save is too far back, you probably left the area--thus Auto-Saving after you hit a bug. Never Save after hitting a bug. Now you know why.
- Reload. Who cares
- Rest. I don't know why this would work, it doesn't sound like Resting would fix anything....but hey, give it a shot.
- Use Shadowkeeper to correct the faulty variable(s). A surefire method if you know what you're doing. I wouldn't know what I'd be doing.
- Use Ctrl-J to teleport your party across the gap.