my Father has been in atrial fibrillation for years. What is going to happen will his heart just give out???

Have you spoken with his doc? My mother has lived with this for years. She has a pace maker which controls rythm. However, most of her docs think she could do without it.
In my Mom's situation, the heart works harder and has now expanded. The muscles also get tighter and thicker.
I am not sure of the outcome...each heart condition is so different.