As for how the original Rufio is still alive as an adult in 2017 after dying at the end of the blade of Captain Hook, there's an explanation for that. Rufio may have died in Neverland back in 1991, but all that did was return him to his body on Earth.

Did Rufio really die?

He is mortally wounded in a one to one duel with Captain Hook. Before he dies, Rufio tells a mortified Peter that he wished he had a dad like him. It is Rufio's death which ultimately forces Peter's son, Jack (who had been temporarily brainwashed by Hook into hating his father) to realise Hook's true cruel nature.

Who kills Rufio?

Killed by Hook. Rufio was a Lost Boy killed in Neverland by Captain Hook.