In bold italics is what happened in the actual book.
What could have happened
"Maybe I can visit you," I said.
She shook her head. "No man ever finds Ogygia twice, Percy. When you leave, I will never see you again."
"But—"
"Go, please." Her voice broke. "The Fates are cruel, Percy. Just remember me." Then a little trace of her smile returned. "Plant a garden in Manhattan for me, will you?"
"I promise." I stepped onto the raft. Immediately it began to sail from the shore.
As I sailed into the lake I realized the Fates really were cruel. They sent Calypso someone she couldn't help but love. But it worked both ways. For the rest of my life I would be thinking about her. She would always be my biggest what if.
A couple years later after the Titan War
"PERCY!" he heard Annabeth scream as he fell. As he fell from all his friends and things he cared about; as he fell from his life. He was sure he would die, there was no way he could survive.
Unless... No, he pushed the thought from his mind. He was crazy for even thinking it; he would never land there, she told him herself, no man ever found her island twice. Or so she thought.
She knew it was him, it had to be. But how was it possible? There was no way he could land there twice.
But she knew as she looked down at green eyed, black haired boy that she had pulled ashore, it was him. For the first time ever a hero found her island twice; and it just happened to be her favorite hero that she loved the most.
Perseus Jackson.
For days she helped him, nursing him back to health. She savored the moments he was here, as she knew that he wouldn't be there long. That is, if he chose to leave.
Percy woke up confused. What had happened? Where was he? And why did this place seem so familiar?
He looked around him at the cave. He had definetly been here before, but he couldn't remember when. It was all a big blur.
Percy stood up and walked around. He didn't leave the cave though; he had no idea what was out there. But for some reason he felt like there wasn't any monsters out there, in fact he felt the opposite. Percy felt like there was someone out there that he loved.
Then all of a sudden it all came rushing back to him. The fight, falling off the cliff, no one being able to save him. He thought he was going to die but he landed here. Ogygia.
But right that moment he wasn't thinking about how it wasn't possible he was there again. All he could think about was the girl who lived there. Calypso.
Percy would think about Calypso often; he would about her island that she was forced to stay on forever and how she fell in love with each hero who came. Sometimes he regretted leaving her, making the choice to go back and help win the war. Life would have been easier and happier on Ogygia; Percy wouldn't have had to see so much death and have that feeling that he was the cause of it. All because of a prophecy.
He realized he would have to make the choice again, if he wanted to stay or if he wanted to leave. What he decided could change his fate.
Percy walked outside slowly and saw Calypso standing on the beach looking out at the horizon. He walked over and stood next to her their shoulders touching.
"It's really beautiful isn't it?" Calypso said looking at Percy, "I love watching the sunset, I find it calming."
They fell into silence watching the sunset together. Percy felt a special connection with Calypso, a connection he didn't feel with anyone else, not even Annabeth. He didn't know why he liked Calypso so much. It wasn't because she was beautiful, although she really was. There was just something about her personality that Percy loved.
Calypso sighed unhappily,"I hate to bring this up Perseus, but you must decide. Would you like to stay on Ogygia, be immortal and live with me forever?"
He wanted to say no, he loved Annabeth and wanted to have a life with her. But at the same time he also loved Calypso and had always wondered what would happen if he said yes; now he could find out. He was torn, but Percy knew deep down he had already made a decision. He wasn't sure if it was the right decision but who said he had to make the right decision? He was following his heart.
"Yes," Percy said slowly. "Yes, I'll stay."
And he did. Did he regret his decision? Well sometimes he wondered if he should've left, thinking about how his friends must've felt but all in all no, he didn't regret it. He loved Calypso and Calypso loved him. It was meant to be.
They lived happily ever after.
