Complex sentence: The group recorded a demo in 2000, followed by the departure of vocalist Robert Colnik, later replaced by Markus Keller; who re-recorded a track from this same demo with his vocals.
Split into simpler sentences: The group recorded a demo in 2000, the departure of vocalist Robert Colnik followed shortly afterward. He was replaced by Markus Keller; who re-recorded a track from this same demo with his vocals.