I'm not going to go into detail on this topic at this time, but if your kitten or cat is diagnosed with FIP, chances are your vet is going to suggest euthanasia.
But, FIP is no longer a death sentence. Visit http://fiptreatment.com for more information.
The treatment can be costly, but you don't have to buy it all at once, and there is the option of crowdfunding to help pay for the costs of medication to make it more affordable.