<< ouside...
i.e. Garage/big fields with lots a field mice... stilll fed ect.. not abandoned.... >>
Life outside is still precarious. Even if the cat is up to date on all vaccinations (more necessary for outside than for inside cat, exposed to more outdoors), has its claws and in in good general health, is treated regularly for fleas and ticks (can't be outside w/o getting fleas, especially during summer), it's still up against the automobile, neighborhood nuts and cat-hating neighbors.
Did you read the thread where someone said they'd gladly kill a cat if they saw it up on their car/scratching the paint? That's just sample of what cats are up against outside.
For the past 10 or so years we have had 5 indoor/outdoor cats - one was found in a the city trash clubbed to death, one simply disappeared, one was killed by an automobile, the remaining 2 cats are indoor only now. I hope your kitty fares better than ours did.