Sorry to hear about the issue that you experienced. I've been doing this for a lot of years and I hate to say it but sometimes how long your engine lasts is just a crap shoot no matter what brand it is. However for a glow plug element to come apart your tune had to be off. Either the engine was simply too lean on the HS needle or the needle balance which I often talk about was off and you had a lean LS and a rich HS (which would show a normal temp) but in a nutshell excessive temperature is pretty much the only way that a glow plug element will melt and fall apart. Once the element falls into the engine and the motor is ran the element can bounce around and chew up the entire engine in minutes.

When the plug fails while driving you will normally feel a change in tune and your motor will start feeling rich. Any time that you notice your plug is dead I would advise that when replacing it always take a second to check the old plug to make sure that the element is intact. If you find that part of itis missing sometimes the element passes though the engine and just gets blown out the exhaust port without any damage. Sometimes it gets stuck in the exhaust port which will then cause the engine to seize, sometimes it gets bounced around in the combustion chamber damaging the head button and piston top. Either way though any time you pull the plug always take a second and inspect the element and if part of it is missing pull the engine apart and inspect/clean out the internals just to be safe.