Slick I am so sorry to hear about Max. I would also be worried about the peeing as kidney kitties pee a lot. I am surprised to see how many pee-cakes Filou produces per day.
Of course if he loses weight that really makes it difficult for him to jump. I can see it in Filou who instead of jumping first to the table then at your shoulder now climbs you as if you were a tree.
Poor little boy.
And while if the worst happens you should not think of staying petless there is still only one Max. As there was only one Tigris.