Many spouses who are truly "soul mates" have such a connection that when one passes away, the other really doesn't want to live without his or her partner. Even with a loving extended family or grandchildren, there's not a lot else for them to cling to to want to live without their true love.
I am solely believe that people do lose their will to live when their spouse dies. When you think about what is in a spousal relationship, particularly among long married couples, it doesn't surprise me one bit that a spouse what just quit wanting to live after his or her spouse had died.
I think that in the case of some people, when your whole life is built on your significant other, their death can be devastating. When a parent loses a child it tears them apart. However, people tend to realize that even though a loved one is lost, life can still be worth living.
Although I have heard of this happening on more than one occasion either in the news or in my own family, it's still just coincidences. I've also heard stories where people have lost their significant other and lived ten to fifteen more years. Some even get re-married. Its a sweet story to hear but there is just not any proof.