I'm not an advocate of un-level ground, but will share my recent experience.
Our 18' Ultra Frame is roughly 1 blue square out of level. Just slightly less, which is probably 1" or so, I've never been concerned enough to measure.
Our pool gets very hard use by a large group of 8-13 year old kids. On the last day of school we had my daughter's entire 5th grade class over for a pool party. Let me tell you, that pool was jumpin' and rockin' ! After that day it was obvious that my particular un-level situation is not going to be a problem. If it didn't fail that day it never will.
So yes, do make every effort to get your pool level. But if you have an Ultra Frame and it's 1" or so out of whack, chances are you will be OK.
Back to your original question, I believe that I have seen at least 1 story of a pool collapsing but don't recall the details.