I see that Adolph seems to be missing from censuses after 1891 , although Marie's marital status is not shown as widow.
Also that when daughter Marie (Marie Johanna) married John Wilson Allan in 1903 her father's name is shown as John Adolph Hermann.
There's a newspaper report in 1895 of an ill-treatment case brought by the wife of Johann Adolph Hermann, 49, a German, of Seaton Street (Morning Post, 18 April 1895). She said she had been married to him for 26 years and had been subjected to great brutality. He was given 3 months hard labour and bound over for 12 months.