Maybe you'll think of me when you are all alone
Maybe the one who is waiting for you
Will prove untrue, then what will you do?
Maybe you'll sit and sigh, wishing that I were near
Then maybe you'll ask me to come back again
And maybe I'll say "Maybe"
That is dead on to the feeling of the Vault Dweller. He being all alone in his adventure to save his home. Knowing that Vault 13 is waiting for him. Vault 13 does prove untrue to him and what did he do? And in the last scene, the Vault Dweller walks away defeated. You can tell from his head bowed that he was crushed and in a very honest possibility he would have asked himself if they wished he come back again and knowing from all the pain he endured until his final judgment that in his heart he knew that just maybe, he'd say maybe.
I told the Overseer of Vault 13 I'd give everything to save everyone, and so I did, I saved them all. Since then I've felt loneliness.