I wuld suggest trying to locate Mary's grave, assuming it's located in Duluth, Minnesota or Carlton County, Minnesota. Their son may be buried next to her. You may be able to get his name that way.
If Victor was single in 7/1917 (per WWI draft registration), I'm assuming they were married between July and December 1917, in either St. Louis County or Carlton County, Minnesota. I couldn't locate their marriage info. Familysearch.org should have a listing, but there may be a transcription error with their names.