I have just been through something like this with our 16-year old Siamese cat Beeper (chronicled on Thread Drift). She did pull through and although I know we won't have her forever (Vet on the ultrasound: "Her kidneys look like swiss cheese"), she is doing reasonably well for now on subcutaneous fluid twice a week--still enjoying life. So know that you can still get a reprieve with an older, very sick animal. And also remember this quote that our vet sent us after we lost a well-loved cat:

"We who choose to surround ourselves with lives even more temporary than our own
Live within a fragile circle, easily breached
Unable to accept its awful gaps, we still would live no other way.
We cherish memory as the only certain immortality
Never fully understanding the necessary plan..."

The Once Again Prince
from
Separate Life Times, Irving Townsend