I would say this is Leah's death so he was still married but might have done a runner.
Civil Registration event: Death
Name: SIVITER, Leah
Registration District: Help Dudley
County: Staffordshire
Year of Registration: 1878
Quarter of Registration: Oct-Nov-Dec
Age at death: 71
Volume No: 6C
Page No: 15
That 1851 census certainly looks like him.
1851 census transcription details for: Halesowen Road, Dudley
National Archive Reference:
RG number: HO107 Piece: 2033 Folio: 541 Page: 22
Reg. District: Dudley Sub District: Dudley
Parish: Dudley Enum. District: 1M
Ecclesiastical District: St Andrew City/Municipal Borough: Dudley
Address: Halesowen Road, Dudley
County: Staffordshire
Name Relation Condition Sex Age Birth Year Occupation , Disability Where Born
HACKETT, James Head M 28 1823 Nailor Rowley Staffordshire
HACKETT, Ann Wife F 26 1825 Nailor Rowley Staffordshire
TAYLOR, Thomas Son M 6 1845 Scholar Rowley Staffordshire
HACKETT, Maria Daughter F 2 1849 Rowley Staffordshire
SIVITER, John Lodger Unmarried M 45 1806 Nailor Rowley Staffordshire
HACKETT, Thomas Lodger Unmarried M 23 1828 Nailor Rowley Staffordshire
HACKETT, Mark Lodger Unmarried M 66 1785 Labourer Rowley Staffordshire
But then there is one of mine who I have not traced much...
http://bcconnections.tribalpages.com/family-tree/bcconnections/115313/77908/John-Siviter-Family