Just like in people, all surgery and anesthesia has risks. Some cats may be sensitive or allergic to a particular type of anesthesia or may have a preexisting condition. The vet will probably offer pre-operative blood work--I would suggest doing this as it verifies that liver, kidney, and blood values are within normal before surgery. Most cats handle anesthesia well, and there are risks to not having the teeth cleaned as well, as broken and infected teeth will allow bacteria into the bloodstream, where it can damage organs, including the heart, kidney and liver. Painful teeth can also result in a cat not eating.
I would talk to the vet beforehand about your concerns. Find out which anesthetics will be used. Certain anesthetic agents are safer than others as they are processed differently by the body. I have had surgeries, mostly dentals, performed on three of my cats. None had any complications, and the youngest of the bunch was 9 years old--the others were much older. Odo has had three dentals in the past 2 years. Spot had a dental and a couple of other surgeries--he also had risk factors like hyperthyroidism and heart disease. Willow had surgery when she was very ill so that a feeding tube could be inserted. None of the cats had complications related to the surgeries. I did do research before most of them (except Spot's--I didn't know there were options back then), and I made sure my vet was using the anesthetic agents that I believe are the safest, propofol and isoflurane.
Every surgery has risks, but I feel that the need for the surgery usually outweighs those risks by improving the quality of life for my cats. The following links may be helpful to you:http://www.veterinarypartner.com/Con...=11&A=1607&S=2http://www.lbah.com/anes.htm