I am so sorry for your loss. This hits me so close to home. I don't have the same guilt of the accident, but having just put my 17 year old cat to sleep on 7/10--I feel the guilt for all the would of, could of, should of's...
It is a terrible loss. I am sure your kitty was well loved. But nothing can change/erase the pain and loss. My heart goes out to you!