Oh my.....please don't euthanize him for luxating patellas. They really are not as painful as one might think...unless maybe he has a torn CCL??? If he has some discomfort at times, you could give him an anti inflammatory such as Metacam or Rimadyl. Speak with your vet about that.
This post made me so sad.
I have older pups with luxating patellas...knees out..and they function Just fine. My surgeon does not recommend surgery on them once they are older because they are still at risk of tearing a ligament...and then they end up having to have two surgeries.
Keep in mind that MOST yorkies have some degree of luxating patellas....I cannot imagine euthanizing them for it.
I DO understand you don't want him to be in pain and/or suffering; but it if is indeed only LP, I seriously doubt he is suffering.
I am sorry you are so upset with this diagnosis.