Bolt on keels do fall off from grounding, severe neglect to repair, bad design to begin with. It happens. If you google "keel falling off" you will get a few hits. I have not seen any hard data on encapsulated keel. I have always been a staunch encapsulated gal, but my husband has brought me around to the bolt on keel logic (can absorb damage better, easier to inspect and repair).
Big problem with encapsulated is you just don't know for sure what's going on in there, and if your keel weeps rusty brown during haul out on a 20 year old boat..
Non production boats, the keels seem to fall off on a regular basis
look at the last two vendee globes.