I hope you are not facing the problem. However, in my 6+ years of career as a geologist, I have seen this happening 5-6 times. Twice on a same job in Pennsylvania.
The first time I saw this in 2007. I was supervising drilling for few really deep 1500+ feet core holes and collecting samples for coal bed methane analysis. The wire-line just broke. The driller was pretty new and he had to pull out 1000+ feet of drill rod to recover his core barrel.
Most recently it happened when I was supervising a straddle packer test. The straddle set up just slipped and went all the way to the bottom. Packer Tests are done open hole. So this time you can not just pull your drill rods to recover the packers (which are pretty expensive). Drillers used regular drilling rods and made dents. They push the dented drill rod on the top of the packer and caught it.
See and save the picture for your reference.
Ankan Basu, P.G.