Complex sentence: The current St Hilda's Church was built recently as a replacement for the older, larger St Hilda's Church on the same site, which whilst it stood for many years remained unfinished until its demolition.
Split into simpler sentences: The current St Hilda's Church was built recently to replace the older, larger St Hilda's Church which was on the same site. Whilst it stood for many years, it remained unfinished until its demolition.