There is a burial at St Mary, Paddington Green that could be a decent candidate for John's wife:
17 Sep 1843 Elizabeth Child (of) Boston Street, St Marylebone aged 50
Might be worth getting the death certificate to see what it says about her, particularly as death certificates usually described women as 'wife of' and sometimes also gave the man's occupation.
CHILD, ELIZABETH aged 50 GRO Reference: 1843 S Quarter in MARYLEBONE Volume 01 Page 147