Complex sentence: Their stock was lifted temporarily with the arrival of the self-released "Face To Face" 999's popularity continued to decline steadily, leading to the group disbanding twice in the 1980s, reforming soon afterwards.
Split into simpler sentences: Their stock was lifted temporarily with the arrival of the self-released "Face To Face". Unfortunately, 999's popularity continued to decline steadily, leading to the group disbanding twice in the 1980s, only to reform soon afterwards.