It's pretty much impossible after the Hundred Days. He was seen as too much of a liability, even before that; one of the reasons he decided to MacGuyver his way out of Elba was that he heard rumours of a plot among the victorious allies to ship him out to the mid-Atlantic anyway.
And as said, there's no real guarantee that Marie Louise would take him back. Especially under Austrian supervision; even her son from Napoleon wasn't safe.
Nah, your best bet for a Napoleon living as a free man is if he escaped to the United States, which he considered doing after Waterloo. Rather than seeking asylum aboard the Bellerophon and becoming a prisoner.