Upon occasion, one hears fellow genealogists being slightly judgemental about a specific ancestor. Instead of getting bogged down in that line of thinking (which doesn't help your research any), think "why?"
Putting yourself in your ancestor's shoes gives you a different perspective. If you were twenty-six years old, widowed, the mother of two small children, unable to speak English and living where you had no relatives, what might you do? You might marry the first German speaking single male around--one who would not have been your choice if you were twenty years old and still living at home with no children to support.
If your great-grandfather "disappeared" consider where he might have gone and what he might have done in an attempt to find him. Was there a war he might have enlisted in? Did he have some type of psychological problems? Maybe it was even better that he left, despite the disruption it caused in the family.
If you never personally knew the ancestor, leave the judging to someone else. Focus instead on your research.
On the flip side of this, I know one researcher who thought it was "romantic" that her great-great-grandmother found the "love of her life" and left her husband and headed out West on some grand adventure. The researcher was completely enamored with the story. Now if HER mother had done the same thing, I'm certain her response would have been somewhat different.