They pop back in with a bit of a push. Not easily but not overly hard. I ripped the whole screen out of the back of the camera body when disassembling my broken K-1. I would send the camera with the lens for checking after such accident, it does not take too much force to misalign the lens mount in relation to image sensor.
BTW, the tilt screen is able to withstand huge abuse without legs slipping out of the guide rails:
That skeleton construction weighted about 17kg in total and it was hanging from the tilt screen supported by nothing else. So it takes a formidable force to make those joints fail.