I'm very sorry for what your Snowy went through while you were on vacations.
Hopefully with time and lots of TLC your Snowy will go back to his happy and relaxed self.
No doubt the experience has been traumatizing and quite stressful and given the fact he has been deprived of a good source of food for the two weeks you were out, you need to pay close attention to him and to keep on encouraging him to eat his food. You can also offer him some egg food to help him out during this time.
It would also be good to have your Snowy examined by an avian vet specialist, because depending on the level of malnourishment, he may need supplements/vitamins.
I'm wishing your Snowy a steady and full recovery.