Technically having the retail disc is pointless because the game is kinda like an APP on the PS3 that's completely digital. The only use that comes from the disc, is that it has the installer on it for the game. It doesn't play the game from the disc, so you'll only need the disc for a few seconds. Alternatively another disc exists that gives you the rundown of Final Fantasy 14's storyline for PS3 players that never got the chance to play the original game, having been exclusive for the PC.

My guess is that when it becomes available on PS4, it will be a free download from the store. Perhaps SE will provide you with a code so that it's free of charge.