Hi clairdavas,
How long can you live with kidney failure? - without treatment a very short time measured in weeks (two or three at the most), is the usual answer.
It is almost inevitable that stage 4 will become stage 5.
The kidneys are on their last gasp in stage 4 so inevitably they progress to stage 5.
The only question is when, the time scale depends on the root cause of failure, and the individual.
The 'cure' is a transplant, life can be sustained, and the patient kept healthy enough to undergo a transplant by dialysis.
Dialysis can, and in some cases, doe's keep people going for tens of years.
The situation is made more complicated because kidney failure weakens the immune system making the patient more susceptible to other health issues.
There is some very reliable, and useful information on these websites;
http://www.kidneypatientguide.org.uk/contents.php
http://www.edren.org/ explore the 'hand book'.
Any information you find on the internet should be treated as suspect, until you are sure it is from a reliable source, there is a lot of rubbish out there.
Best wishes.