Hi Cindy - I'm really sorry to hear your cat is unwell. Are you able to answer these questions please?
How long have you known about the renal disease? Did he have any blood tests? Do you know the results?
In general terms, until near the end, renal disease is not painful. By drinking more water cats are able to compensate for the loss of kidney tissue. Unfortunately there comes a time when even when drinking more, the toxins start to build up to levels where the cat feels nauseous and will often start to vomit. If she has stopped eating and drinking then it may be that your cat has got to this stage.
Some people have very strong views on euthanasia, and it is a subject that you need to be guided by your views and conscience. My personal feeling is that if we are able to prevent animals from suffering, then we should do so, even if it means having to put them to sleep. We know from people's own experience that terminal kidney disease does make people feel very ill indeed, and i think that a quiet injection (when you can hold him and be with him) would be a better end than dying 'naturally'.
Depending on the test results, it is of course possible that her illness may not be related to her kidney disease, and your vet would certainly be able to discuss with you whether you wanted more tests done or whether you felt it was time to let him go.
I hope this helps. Do let me know if you need more information.