My cat is 17, adopted last year. Generally lively, no obvious signs of distress or pain besides mild arthritis.
She used to throw up a lot, and after a battery of tests the vet declared that she was almost certainly just allergic to something in her diet. They prescribed hypoallergenic food but unfortunately it seems she would rather starve than eat it. It is wet food, as she generally refuses dry food. I introduced it slowly with her regular food, I tried heating it a little, I tried topping it with treats; none of this provoked any interest in it. The only thing that worked a little is if I pretended to eat it, but then she only licked a little before walking off. She is clearly hungry and continues to demand food.
After two days of her not eating I bought her a tin of tuna in fresh water. She loved that and ate it all immediately, and so far hasn't thrown up.
I did try cooked salmon and cooked chicken, but she wasn't interested in eating those.
I know that tuna is not nutritionally complete and also contains a lot of mercury, however at 17 maybe I should just accept that my cat is on the way out. Certainly I don't want her to starve to death and it's better she eats tuna than nothing.
Let us assume for now that the vet is correct and she was throwing up due to allergies. Also let us assume that these allergens are in the cat food she prefers. Are there good options besides tuna?