On neopets when and where did Derek Pteria die?

Derek Pteria did not die in Neopets. He is a fictional character in the Neopets universe, and his existence is entirely within the context of the game.

There are no official accounts or events within Neopets that suggest Derek Pteria has ever died.

It's possible that you are thinking of a different character or a fan-made story within the Neopets community. If you can provide more details about where you encountered this information, I may be able to help further.