Sorry for your loss FireShadow, my thoughts are with you.
We have 2 cats now 'April' and 'Roo'. They are both indoor/outdoor as we agree with you.
Woulda, coulda, shoudas will only eat at you if you let them. They may be the result of the predator's mind trying to suck more energy from you. Learn from it but move on.
'Sammy' our cat we had several years back, was attacked while outside by what we believe was either a raccoon or a possum. We tried for a couple weeks to save her with doctors, surgeries, medicines, etc. while a tube was inserted to continually drain one of the abscessed major wounds. But it was all to much for her and she passed. It was an emotionally difficult time.
Sammy was so gentle and curious that she probably walked right up to and surprised her attacker. Her nature that may have took her life is also what we remember most about her. She tried to be a friend to all. She never killed or brought 'presents'. She allowed mice to be right in front of her and tried to lift moths (yes lift, she never batted them it was more like getting her paw underneath and lifting up. It was astonishing to see)
We "coulda/shoulda" for a while afterwords and did not allow April outside. This only depressed April (and us) more (she couldn't find or play with Sammy when she wanted to). We finally felt we did the best we could and allowed April out because why punish her.
JH