I think it would Vary depending on the Monster Species, if they are true romantics, then they'll mourn and starve themselves to death to join him in the afterlife, or the more gothic horror loving types would try necromancy. Other monster types might gives themselves time to mourn and hold a funeral, but then I can see them looking for another husband. With monsters that have harems, I think she'd be sad, but then after a bit she'd start sexing with her other husbands.