Very sad.
I'm glad I had my cats chipped. Didn't do it for a while as adult son put doubts in our minds: 'first it is pets, then it will be adults'. That sort of thing. That was many years ago. After our youngest cat (who is now about twelve, we took him in as a stray), still very active and though we had him neutered, still thinks he's a tom cat sometimes, bless, was in an accident and ended up at local vets after someone was good enough to do a bit of research, we had them all microchipped. Hee hee, by that time son, who was a few years older, said nothing!
Since then our youngest cat has had another car accident and we were informed almost immediately. Also met and thanked the person who took him to vet and we changed vets to be with the one who treated him, who was great.
Well he still goes out on the prowl, less so of course but it happens. He's gorgeous. The other two, mother and daughter, don't go out much now now.
Yes I agree pets should be microchipped. I would have been distraught had any of mine disappeared and I never found out what happened. It's caring to do so.
Has to be said that if cats are involved in a collision with car they often somehow manage to move to another place before collapsing. That may be the case with the one you found. I remember years ago seeing a cat completely run over by a car in our road - there was a dent in its back but it ran away and goodness knows where it ended up. It was horrific!