In the 1916 Portland city directory, there are listings for Marie Wolkerstorfer and Mrs. Mary Wolkerstorfer, widow of John, both with home/residence at 589 Karl. Women who were separated from their husbands were commonly listed as a widow in those days, but it would be interesting to see her 2nd marriage record to see if she listed herself as divorced or widowed.
A family tree on Ancestry connects him with various Wolkerstorfers in Minnesota, so maybe there's an obit for a sibling that mentions him.