They do regress, and yes they are harder to train. But it can be done
However, if you truly want him to go, than please find a suitable adoptive family for him. Please do not dump him at a shelter or pound and please make sure his next family is up to the potty training task. You don't want him to be passed around from family to family bc of pee problems. My advice is to seek out a Yorkie Rescue to surrender him to in your area (there are plenty that will take him in and make sure he finds a suitable home for him).