I'm very sorry about your Yorkie, but you got help just like you should have and his chances of recovery are so extremely high.
This surgery is performed quite a bit. He may be on a special diet for life, but that's not a big deal.
The surgery won't take long and he'll be out of anesthesia very, very soon. The ER will just keep an eye on him and he'll probably come home tomorrow or the next day.