I've replaced a decent amount of plugs that shot out. There may be some validity to them blowing out after plug replacement due improper torque, but that's not the whole story. A lot of them were blowing out prior to any plug replacement. It was a defect in both cylinder head and spark plug design. It happened on Ford modular engines in the late 90's-early 00's with the 2 valve heads (4.6, 5.4, 6.8), but for some reason it was less likely to occur on 4.6's. I would drill out what was left of the threads. Vacuum into the cylinder. Start the engine with the plug hole open to push out any remaining particles that were in the cylinder. Use a tap to create new threads. Repeat process of vacuuming and starting engine to remove any debris. Insert new steel thread insert with loctite and swedge it into place. Install updated Motorcraft plug with more threads. Voila. Never once had a comeback or any related issues from this process. Something a lot of people never bring up is that they start making noise a little while before they blow out. It starts to sound like an exhaust leak and at that point, you may be able to torque the plug back up and save yourself the hassle.