There has been reports of both scenarios so I would not rule out the possibility of the lower mount breaking. Some cars even rapture in the turrets as you describe but most of those have been run without a rear strut brace which stabilizes the rear of the car.

I would recommend you install a strut brace if installing coilovers, and if you want to be extra safe then weld some reinforcements onto the lower shock mount aswell.

Ive been running my car without reinforcements for a couple of years now (Gaz Golds 2wd) and there are no visible wear on the lower mount as of yet.