In the 1871 census (at 22 Shore, Ramsey, where she was a Lodging House Keeper) Judith, 40, was a W[idow] whereas in 1861 she was M[arried].
So, if accurate, Henry died between the 1861 and 1871 censuses.
He may have been recorded in the Ramsey parish registers which are not included in Brian Lawson's burial indexes, but are available on LDS film through Family History Centres worldwide.

In 1891 Judith was 62, Wid., Private Means, and living at South Parliament St. Ramsey with son Robt E. Gill, 40, grocer, wife Sarah 33 and their children Robert, 5, Thos E., 4, & Edith M., 2.

Findmypast has her death date as 14 April 1893 in Ramsey aged 62, widowed, spouse Henry Gill, painter, Ramsey.
The Maughold parish register has her burial, aged 62, of Ramsey, on 17 April 1893.
There is a will which looks like hers, and could be revealing:
GILL, Judith 1894 Ramsey, [no.] 42, [LDS film no.] 0106518.

FMP also has the death of Robert Edward Gill aged 3 yrs 5m on 21 May 1888 in Ramsey. He was buried in Maughold on 24 May.
And of Sarah Ellen Gill aged 37 of Ramsey d.26 Oct 1895, spouse Robert Gill, grocer, Ramsey (she was buried Maughold 28 Oct.).

In the 1891 census son Henry Gill, 38, grocer, was at Summerland, Maughold, with wife Jane, 48, and step-children Garrett.

Sue