This cat had been with my family since my brother and I found her after one of our soccer games when we were little (about mid-'96 or '97). April last year, she had a stroke completely out of the blue and we took her to the emergency vet to be looked after overnight until we could take her to our normal vet. Both vets said she wouldn't recover and we should just put her down. I said 'no' and we brought her home. After caring for her for a couple of weeks, she started showing improvement, being able to move and walk on her own. Soon enough, she was about as healthy as she could be considering what she went through. She went on to live another year being a pretty happy kitty before she passed away last month. Going from "there's little chance she'll survive, you should put her down" to living happily for a year (she was about 16 at this point), I was really happy for that extra year of being with the cat that was essentially mine. She attached to me far more than anyone else in the family and I miss her, but I'm at peace knowing she had a happy and (relatively) healthy life with me and my family. :)
Oh yes, and the second part. I know that feel of losing a long-lasted family pet oh too well, I've had 3 lost just in the past 5 months. A 12-year old Chocolate Lab, an 18-year old white-orange shorthair cat that never really great to bigger than a couple of handfuls, and my 16-year old calico.
Many hugs your way, HellDunkel.
If I am randomly picked, Clive Barker's "Undying" would be fairly fitting, I think.