I know what you are talking about. Our Filou may make the trip during the next years, having kidney failure, and Tigris looks as healthy as can be. Filou is the one who comes under the covers and warms us. Tigris sleeps on the pillow (or on my knees ). I have no idea what to do in case... I must admit without Pet Talk I would feel like it would be too difficult to introduce another kitty but here there are some good stories: Peanut and CJ e.g.

I am sure Speckles at RB will give you advice.