5. Quinlin Vos - Likely
Quinlin Vos is a character who exists with one foot in and one foot out of canon. First appearing in the Legends comic series, Star Wars: Republic (following a retroactive cameo in The Phantom Menace), he became a favorite of George Lucas. This resulted in two things, the first of which is that the character found his way into appearances on The Clone Wars and by way of these appearances entered the full canon.
The second thing is that George Lucas wanted him to survive Order 66. So, rather than being killed off in the comics, he was allowed to escape and continue his adventures, eventually starting a new life. Unfortunately Disney has rendered all of those events to be non-canon.
The canon fate of Vos has never been addressed but considering how much Lucas came to care for this character it would be completely on brand for his protege, Dave Filoni to confirm his survival in the new canon and bring him in as Grogu's teacher.
Vos is also something of a roguish character and would fit the world of The Mandalorian like a glove. It's even possible Din has already met this guy without ever realizing that he was a Jedi. Considering all of this, the odds of Quinlin Vos returning are not small. In fact, they are pretty damn good.