In my 30 years I have only seen this happen a couple of times. I had rocker arm on an intake almost fall off because the nut came loose. Here is the million dollar question

Why did the lifter stay in its bore?

I was spinning this over 4,000 when I noticed a loss in power. I have always used a valley pan just for this reason. This time I was half done adjusting the valves and forgot to put back in. Now I am wondering if I should take the intake back off and install it.
JIM

Ive broken studs but never had a nut come off. Ive never had a lifter pop out of its bore even after broken push rods. Just lucky I guess.

I've seen alot a valve train failures but never have seen a lifter pop out! I ran circle track cars spinning the motor aroung 7000rpm and have broken push rods & rocker arms under these conditions and the lifter had always stayyed put. I believe that since there is no longer any pressure holding the lifter down its gets pushed up and never has a chance to fall as the cam is just spinning to fast. After the motor sits the lifter falls back to rest on the cam.

I have had a rocker stud come loose before . I started locktiteing them.No nuts though