Fortunately, I haven't had a spouse die (but my mother did, and she was only in her fifties when she did and when my father died at sixty-two). I have, however, lost loved ones (like both of my parents), and I don't think any divorce (that a person doesn't want) could be any worse than losing a loved one. On top of that, there's the whole thing that people who lose spouse through death have added complications tied to both death of a loved one and a devastating and unwanted change in one's life and plans for the future (as well as a lot of other issues associated with being widowed).
I think the main reason a divorce would be hard to get over would be if one spouse loved the other very much and didn't want the divorce. With that, though, real love is supposed to be about wanting the other person happy - not about what we lose. So, if we really love someone; I'd think that at least knowing they're happy should help ease the sense of loss (IF the love we have for them is whole and real and what genuine love is supposed to be). A lot of love, though, isn't as whole and real as people think it is. A lot of it is more about what the other person brought to our life and to us. The sense of loss isn't about sorrow over what happened to them. It's sorrow over what the person left behind lost.