After Peter Haydon was killed, he reluctantly decided to cancel the expedition. However, the damage done to Captain Hopper's rocketship forced the expedition to remain while repairs were made, so he allowed further exploration to be made in the meantime.
It was only when Klieg killed John Viner that Parry realised that Klieg was dangerous. He helped the Doctor seal the Cybermen back in their tombs and left the planet when Hopper's ship was repaired. (TV: The Tomb of the Cybermen)