This is my opinion, essentially, although I did a bit of reading up on it before putting pen to paper. Cats don’t decide to ‘isolate’ themselves to die. It’s the wrong word. Firstly, in my opinion, domestic cats don’t know that they are dying. They are not making a rational decision to go away to die on their own.
They do know that they cannot defend themselves against a predator because they are injured. And they do know they have to find a safe place to protect themselves from predators. The domestic cat is behaving as a wild cat. They don’t recognise the fact, under the circumstances, that they have a human home to go to for help (when the injury occurs outside the home).
And so domestic cats find a safe place to protect themselves when they are badly injured or very ill. There is a complication here because if a domestic cat is very ill, they will normally be treated by a veterinarian with their owner’s help. There is no opportunity to find a safe place to hide. The concept of finding a safe place to hide really is about indoor/outdoor cats and the cat being outside and getting into trouble. Or they live in a household where the owner is absent and unconcerned, perhaps even negligent.
They don’t do the same thing if they are dying of natural causes in my opinion. Domestic cats will find a safe place for protection if they are seriously injured but not if they are dying of natural causes, but it depends upon whether they are dying of old age (general failure of the body’s organs due to old age) or of a specific illness in my opinion.
I think this is a correct assessment because, as mentioned above, they don’t know that they are dying (disagree with me? Please leave a comment). And therefore, if they don’t feel pain, they don’t feel vulnerable and if they don’t feel vulnerable there is no need to find a safe place to protect themselves. Under these circumstances they will simply stop breathing wherever they are.
This is why you read stories of domestic cats dying of old age anywhere in their owner’s home. It might be in their favourite place or in the kitchen or on their owner’s lap. They suddenly pass away perhaps during the night and their human caregiver simply discovers them.
But if they are injured, they will do their best to find somewhere safe which affords them protection, to allow themselves time to gain their strength and to heal themselves. They are not predicting into the future that they will be able to heal themselves. It’s all instinctive. They just instinctively know that they need to have time in a safe place to try and get back to good health. They may well pass away at that place and often do.
They do not go away ‘into isolation’ to hide from associates (friends) but from predators. Although I would appreciate the views of others. I did a quick search of the Internet to see what other people thought and, by and large, the general mood is as I stated on this page.