There is a death of a Mary Turton in 1856 aged 37 years (seems to tie in nicely with the age on the 1851 census) she was living at Button Lane and buried at Brammall Lane St Mary's
Did John Snr remarry? I have found a burial for a John Turton on 24 Jan 1889 (aged 72) living at 23 Regeant Terrace, he was buried at Ecclesall All saints. Could this be your John?