Complex sentence: His entombment in a Calatonian burial suit and metal vault lasted thousands of centuries: after being killed by the Radiant and subsequently undergoing the impact of the casket on Earth, his body was sealed underground in total darkness.
Split into simpler sentences: His entombment in a Calatonian burial suit and metal vault lasted thousands of centuries. After being killed by the Radiant and subsequently undergoing the impact of the casket on Earth, his body was sealed underground in total darkness.