Looking up the longest videogame scripts on this link over here: http://gaming.wikia.com/wiki/List_of_longest_video_game_scripts
Looks like I was wrong about New Vegas, it was 65k lines. Fallout 3 also had 40k. Fallout 4 looks set to beat even a whole bunch of games with unvoiced lines, making it one of although not -the- longest game script in gaming so far.
This is really exciting. I think I heard somewhere that the gameworld is going to be 4x the size of Fallout 3, and I even have trouble imagining just how big that would make the game. That 20 million sales from Skyrim really made a difference, and this year is a wonderful year to be a gamer.