Hi Luc
Do you have Joseph's death cert?
If so, does it say if he was married, widower, or when it names the spouse, if she was deceased?
It isn't always stated, but sometimes it is which is a great help......
I did however find this reference to a Probate Record at Archives NZ
Agency = ADBY
Series = 17543
Accession = W5411
Box/item = 6
Record = 207
Maybe someone who lives closer can check this out next time they are visiting, as hopefully it will give details of family members (and therefore if his wife is still alive)
Bren