If someone wants him I think he'll be back. I don't know the specifics of getting out of his deal with Miami tho.
Miami can get out of the deal if:
1. A year from the original date of injury / disability (i.e., February 2017) Bosh still hasn't been medically cleared to play;
2. An independent doctor chosen jointly by the NBA / Union agrees that Bosh can't play;
3. The Heat waive Bosh;
4. Bosh is unable to play 10+ games in any season for another team.
If Bosh plays 10 games, he then goes back on Miami's books, except they no longer have his services.