He cannot have fallen into the sea when Beleriand was ruined. It was already ruined when the Valar retrieved the Silmarils from Morgoth, and it was after that that Maedhros and Maglor stole them.
There is no indication in the Silmarillion or any of the other writings that Maglor's fate was ever lifted. He wandered "ever upon the shores" - that rather sounds like eternity to me. Dying would have meant returning to Valinor, and I feel he did not think he deserved that. It was his own self-imposed punishment, together with the shame and despair.