I too have gotten the "this happens" response from a vet. I then proceeded to say every bad word I've ever learned to him.
This is may. She and her sister June were both taken in for spaying. June was over anesthetized and died. That's it! That's all I got. I was a wreck.
There's nothing we can do. Just like when we lose out family members. We mourn and move on. What can we do, sue everyone? that's not practical or realistic.