Oh my god, FIP? I couldn't follow this so I don't 
know what and if you mentioned any symptoms? I 
had 2 cats die of FIP, so pray it's that 
lymphoma, which is very ugly too, but it seems it 
can be treated. I hate hearing of cats die, 
especially of FIP. So let's hope it's not FIP.

Check here for lymphoma and its possible 
treatment I looked up for you:
http://www.vetmed.wsu.edu/ClientED/lsa.html

I and my 5 cats are with you :)

Ore-sama