I want to say that my pom has similar issues. We've had one knee operated on twice already, and the vet said it is only a matter of time until the other knee will need something. However, she's not shown any pain with the second knee. Futhermore, the first knee is totally back to normal! We don't play any games that require quick stops/starts or quick turns (e.g., ball throwing). But other than that, she is perfectly fine. She is almost 10, as well. Little dogs have a very long lifespan - I don't expect her to go anywhere for quite some time. This type of problem is really, really common in these little dogs. However, little dogs are also better at recovering and adapting to these problems because they have such a small amount of weight to begin with! When my dog was hobbling around on three legs (before the surgery), it didn't seem to bother her too much (not that I advise this - it came on fast and we were in the process of scheduling the surgery). I think my dogs has some arthritis already, and she also has liver issues. But she is happy as a clam! And all this defensive talk means a lot coming from me - my dog is the most annoying dog in the world. I love her, but man, my life would be much more peaceful without a dog (but I do love her lol - she is just super needy and annoying all.the.time).
All this to say - I wouldn't put my dog down for these types of surgeries. They are almost to be expected in these small breeds, and I think they are part of the responsibility of having a breed like this. After both surgeries, my dog was using her leg one week later. They encourage immediate use of the limb in these surgeries, so it won't be like your dog will be in a cast for months. I think little dogs (even at 10) have the ability to quickly bounce back from surgery like this.