He died before 1869 because his wife was a widow at death.  Nothing found in Wills Calendars 1858 onwards.  (What wife?  I have clearly moved his wife!)

He is scored out of the GVRBs in 1886, replaced by Mary Jane Gordon.

Must have died before 1886 as his father's land passed to his wife in that year.  No death for a Robert Gordon before 1886 at RI, IG, GRONI, except the one who died in 1883 and his PAD was a Jane Gilmore, and I think that is a different family of Gordons.