Complex sentence: By the 1980s the mosque been outgrown by the booming Muslim community and had fallen into disrepair, and the city, which owned the land on which it was located, was contemplating demolition of the site to expand a hospital.
Split into simpler sentences: By the 1980s, the mosque been outgrown by the booming Muslim community, and had fallen into disrepair. The city, which owned the land on which it was located, was contemplating demolition of the site to expand a hospital.