I understand. I'm a worrier about these kinds of things myself, and did have to go through it with my beloved, beautiful Rookie, who we had to have put to sleep in 2008 because of epilepsy. She was only 3, so needless to say, I didn't see it coming.
When you think about these things in the abstract, I do think it's harder than the reality (even though obviously, the reality is very hard too). In the abstract, you're thinking of your healthy kitty. If something happens where you had to have her PTS, she would have a serious illness with symptoms, and while it's very hard, you'll understand why you're doing it. It at least makes sense. That's the part you're not seeing now.
Another thing you may not see now is the tremendous amount of support and sympathy you're likely to get if it happens. When my father died in 2003, I got one card in the mail and only a couple friends who showed up to the funeral. When Rookie died in 2008, I got page after page of sympathetic responses here on the Forum, and an outpouring of sympathy from friends. Go figure. I guess enough people have lost pets, and there has been enough on TV and other places about "losing a pet is like losing a family member," that people really do get it. I've tried very hard to do the same for people who have lost pets since then.
And ultimately, you do eventually adapt to the loss. I found the 1-year point was kind of like taking a magic pill. I reached a point where I could remember Rookie, talk about her, and look at her pictures without choking up. That was a big milestone. And now we have the wonderful goofball Murphy, who brightens our house every day.
