Complex sentence: The last queen of the githyanki, Vlaakith CLVII, died after ascending the throne without giving birth to an heir, but returned as a lich, a type of undead, and has ruled the githyanki for over a thousand years.
Split into simpler sentences: The last queen of the githyanki, Vlaakith CLVII, died after ascending the throne without giving birth to an heir, but returned as a lich, a type of undead. Vlaakith has ruled the githyanki for over a thousand years.