Hello. Thanks for the question.
I'm sorry to hear about Bailey. In an older cat like this with significant weight loss, there are a few things that I would want to rule out.
The first is Hyperthyroidism. This is where the thyroid gland is over-active. That leads to increased metabolism and subsequent weight loss. It's diagnosed with bloodwork. The treatment is with meds to decrease the thyroid function or to chemically ablate the gland or surgically remove it.
The next is kidney disease. Chronic kidney failure is very common in older cats and can cause weight loss, decreased appetite, vomiting and dehydration. Often times it's dehydration that leads to crusty eyes as the tear production is less watery than it should be.
Lastly, I would rule out diabetes. Most of these cats are drinking excessively as well, but it's worth considering in any older cat with weight loss.
I would get an exam and bloodwork to start ruling out conditions and find out the underlying cause here. From that point, specific treatment can be started.
I hope this helps, let me know if you have any other questions.