I guess every cat's situation is different but I've had 3 elderly cats (14 years up to 16 years old) who had to undergo surgery, 2 of them had moderate kidney disease/failure......and they did very well. One had kidney disease along with diabetes (he sadly developed a sarcoma on his shoulder and had surgery twice to remove it, though sadly it came back) and his surgeries were very extensive in which they removed a golf ball sized tumor along with surrounding tissue and muscle....and the next week I have a video of him begging for his treats and trying desperately to get the lid off of his can of cat treats :-) Here is video:
I also insist on Isuflourane as the anesthetic. I like Vet clinics that use Laser as there is less bleeding. I always ensure they have a full pre-anesthetic screen (bloodwork) prior to surgery though in the case of cats with CRF and diabetes (however diabetes was well controlled on twice daily insulin and had been for 5+ years), even though BUN and Creat were elevated, I weighed the risks and benefits (particularly in case of having a bad tooth and needing dental/extraction) and we were still fine.
Some Vet clinics don't monitor a cat's blood pressure while they're under and that's atrocious to me.....they simply use a heart monitor. I insist on BP monitoring because a blood pressure can drop quickly and without proper monitoring, too risky.
Some Vet clinics here, or at least used to, would offer a client the "option" of having an IV in during surgery. I wouldn't dream of NOT having an IV in place for if any issues arise during surgery, they need immediate IV access and just as in humans I can't imagine NOT having one. Frankly I wouldn't use a clinic that gives a client this "option". I know we'd all like to save money but this shouldn't be an option, it's critical to have in place....for emerg delivery of meds, if blood pressure drops and fluids needed, etc.
Years ago I rescued a very old siamese girl, weren't sure of age but though to be about 18 yrs old. Found her very ill and weak with CRF and other health issues including horrible teeth, and she ended up developing an anal gland abscess. She also had a rare condition called Hyperaldosteronism which made everything a challenge. She underwent surgery twice....once for the much needed dental and extractions, and a few months later to drain the anal gland abscess. She did well with both.
I think a lot of the risk is related to competence of the Vet staff and those administering (and monitoring) the general anesthetic and vital signs while under. In an elderly cat, just as it is with an elderly human, they are more sensitive to medications, kidney function is often reduced/impaired......so giving "enough" meds to anesthetize properly while balancing with "not giving too much" is critical.
I'm very sorry for the loss of your dear kitty.