Disclaimer: The Mario series is owned by Nintendo.
Reassurance
He woke up within a void of light, floating in the air with no gravity to hold him down. The place consisted of simply a light blue aurora with many small streaks of white light converging into a large ball of said light in front of him. Where exactly was he? The Overthere? He could hear something in the distance, child-like wails that came upon their entry to the world. 'Crying...a baby's cry?' Mario asked himself.
Hearing a familiar giggle, he took a look around in surprise. A projection of the woman who helped him in his search for Peach appeared before him, towering over him in size. "Rosalina!" Mario exclaimed, the woman in question taking hold of her staff.
"Do you hear the baby stars?" the projection asked. "These newborns will grow up to become galaxies someday."
"Baby stars..." Mario muttered in awe. "Galaxies..."
Then it hit him. "The white Luma!" he exclaimed in concern. "Is he-?"
"When stars die, they turn to stardust and scatter across the cosmos," Rosalina explained. "Eventually, that stardust reforms to create a new star...and so the cycle of life continues. But the cycle never repeats itself in quite the same way..."
Somewhere, there was an inkling of hope in Mario's heart that the Luma that accompanied him on his quest would be okay. "And Luigi? The Princess? What about Bowser? What about...about you?" he asked with worry, the final question he just barely managed to choke out.
A moment of silence soon followed. She soon looked at him more closely, a small and barely noticeable smile on her face. It was time for them to say goodbye...
...but she would never forget what he did for her, the lengths he'd go to ensure that he'd fulfill his end of the offer for her. And she was confident that they would meet again one day.
"So...you'll see," Rosalina bade.
The two floated away from each other while everything in Mario's vision went white.