Here’s an interesting little tid-bit of information; Bethesda have confirmed via their Twitter account that Fallout 4 doesn’t end when the main storyline does, allowing you to continue playing. Better yet, there’s no level cap, so you can simply keep going forever and ever and ever and ever and ever and ever and…look, you get the point.
To fans who’ve asked: Fallout 4 doesn’t end when the main story is and over and there is no level cap. You can keep playing and leveling.
— BethesdaGameStudios (@BethesdaStudios) August 6, 2015
Presumably you’ll eventually run out of stuff do, though, unless there’s some procedural generation going on that keeps spitting out random little quests, which would mean theoritcally a die-hard fan could just keep playing infinately. Well, until they die, anyway. Maybe they could pass the mission on to their kids. Maybe their could be generations raised to simply play Fallout 4.
Maybe I’m overthinking it and getting carried away.