This is just a thought... I don't know what the average life span is for a cat, but 16 seems like a good long life... I had a Yorkie for 15+ years that I loved dearly, she was my only dog, and a year before she died, she had an episode of vomiting blood where when we took her to the emergency vet, they said her kidneys were failing and recommended euthanasia. They gave her IV fluids overnight (and gave me a bill for over $1000), and by the next morning she almost seemed like her old self. I had gotten this dog cataract surgery, too, not that long before that episode, and in retrospect I suspect the anesthesia was hard on her kidneys.
She seemed relatively healthy and happy, outwardly, so I felt compelled to keep her going. She was still eating and still interested in her routines, and I couldn't fathom putting her down under those circumstances. What it took to keep her going, though, was twice weekly saline infusions under the skin to keep the toxins flushed out, I tried to do it at home, but it was too traumatic for both of us, so we took her to the vet for those, and she hated it every time. I kept her going like that for almost a year, and thinking back, I know now that was a mistake. She was suffering during that time, and I made it worse by putting her through treatments that frightened her. It would have been kinder to help her go sooner, and I wish I could do it over and spare her what I put her through. I kept her around for myself, not for her, but at the time I thought it was for her.
Someone advised me once that we interfere and intervene with our pets' natural life course by caring for them in a way they would never have if they were left on their own. Vaccines, complete diet, good shelter, vet care, emergency treatment...not stuff they would have in the wild. She said because of that, it's our responsibility to also intervene at the end of their lives. Now that I have some distance from those events with my dog, I know she was right, and I do wish I had made different decisions.
I don't know how much surgery and treatments would traumatize your cat, or what it's quality of life would be afterward, only you can decide, but I just wanted to tell you my hindsight feelings about that illness/end of life stage with my own pet, and how my perspective changed once I had some distance from that emotional turmoil. I know I will make different decisions with my next dog. It's very hard, but I do think you have to consider what is best for the animal in your charge.