It probably wasn't sagging that killed it. Over time those elements will develop hot spots and eventually the hot spot fails spectacularly spewing sparks and plasma from the failure. It's kind of similar to a plasma cutter for a second as there's the small arc in the element which ionizes the gas and it blows it out from the element and if it hits something grounded I can totally see it punching a hole through sheet metal.

https://youtu.be/EC_6urfu5UI?t=7m40s