1. Dude doesnt have parents or they would have pulled the plug. You stay in long term coma because there is no one to agree to it. Hospitals aren't really big on keeping coma patients alive.
2. After the first year, you can more or less give up on waking up. Its no joke when a long term coma patient wakes up because it just doesn't happen.
3. Gracie had to move on with her own life. MC was dead to her. She didn't want to believe it, but he was. Even when he did wake up and move on with his own life and became successful Gracie wouldn't try and drag him down with her health and the girls.
4. While I know the girls suddenly appearing seems to be a plot hole in this, the girls are grown and capable of taking care of themselves as they had been while she is in her last years. The least she can do is get them to meet their father, and he to them.