"Strobe-light induced seizures are indicative of epilepsy, but those aren't fatal unless they occur while doing something more dangerous than playing guitar on stage. Stroke maybe? Hmm..."
It is not all that rare to die of epilepsy related seizures. Most commonly this results from status epilepticus (a prolonged seizure) that prevents adequate ventilation, stresses the heart or may cause a stroke. There is also a condition called SUDEP (sudden unexpected death in epilepsy), that is less well understood, and is a less common fatal event in epilepsy.
And of course a seizure, even in a known epileptic, may be a symptom of another condition, such as a stroke, brain injury or tumors, toxins etc. And a fall to the floor from seizure, simple faint or drunken stumble can occasionally cause a fatal head injury.