The coordinator of the database for the Friends of Newport and Carisbrooke cemeteries has sent me the details of the newspaper article mentioning John Taylor
Fife Herald Thurs 23 Dec 1875
Drowned in the river Orell, New Zealand, on the 30th of last August, William Graham Taylor, 3rd son of the late Lt Col John Taylor, HEICS, Bengal at one time resident in St Andrews.
So, I think that answers the question as to what happened to William Graham Taylor. It also proves that the man who died on the Isle of Wight was the son of Monkhouse Graham Taylor.