I’ve got a webpage devoted to this issue – at http://home.hiwaay.net/~keiper/indoors.htm
Ratty seems to have a good grip on this . I have a dog and a cat. The dog is outdoors on a (long) lease and the cat goes outdoors at night and sleeps indoors all day. They are of course both well fed and loved. I’ve dogs and cats all my life without any problems, they have always been long lived.