There's no way to know. There's never a guarantee, just a chance.
Last year when I had to put my boy down, even though I knew it to be the right decision it was a more than heartbreaking one to have to make. Even though I knew beyond a shadow of a doubt, to this day I still think, "What if?" "What didn't I think of?". For me that'll never go away, and even though it was right I won't forgive myself for it. Stupid maybe, but I feel like I took away from him the only things he had to give. His life and his love.
If Opal is a strong girl, she will likely do just fine but it can go either way. If Sly had needed surgery and it was $1500 with no guarantee it would still be worth it to me to try. My funds are definitely not unlimited but I would have gone without things to give him that shot. And of course, your situation will invariably be different.
You need to make the best choice for you, and for Opal. No one knows either one of you the way you do. But the long and short of it is this: With the surgery, there is a chance. Without, there is none. And even though you'll have pain meds which will help in the short term, she can't tell you when the meds aren't helping any more. She can't tell you when it's time. I do have to say, that the vet recommended immediate surgery. The longer you wait and bounce around, the more likely it is that the decision will be taken out of your hands.
I am so very sorry you're in this position. I am thinking of you and Opal, and sending positive thoughts your way for whatever it will be that you face.