I did not lose my DH to an accident, but one thing I keep telling myself is: if he hadn't been diagnosed with cancer, if he had kept on with "normal" life, who is to say that he wouldn't have gotten hit by a car a week later? Or that something else awful wouldn't have happened? No, of course the odds aren't likely, but all of you who lost your spouses in accidents I'm sure feel like the odds weren't that your love was going to die in such a random way.
It's hard, especially when we look around at friends or friends of the family who have had long happy marriages, to believe that if this one thing hadn't gone so terribly wrong, that we would have gotten the same Happily Ever After that we see around us. And, of course, if you are young and your friends are young, you don't know what lies in their near-term future, either.
It doesn't change the What Ifs, of course, but maybe there's a nugget in there that might help.