There's a certain point in Bastion where you are warned that, if you continue, you won't be able to go back to the Bastion or into other areas. I played through that point, beat the game, and started a new game in the "New Game Plus" mode. When I started the new game, the game overwrote my existing game, which was more or less expected.
In my current game, I will eventually hit this point again. Once I do, I have two goals:
- Beat the game & get the achievements.
- Challenge myself in "Who Knows Where" with the various idols active.
I would prefer to do it in the order listed above, but at this point there's no guarantee that I'd be able to get back into a satisfactory point in the game. The way I see it, there's one of three things that could happen if I try to enter the game after I beat it:
- The game dumps me in the Bastion right before I entered the zone, allowing me to play through the other areas some more.
- The game dumps me somewhere after I entered the point of no return, thus preventing me from going back.
- The game simply shows statistics/credits/a message saying that I can't go back in.
Considering the events that occur after that point combined with a comment Ben "Yahtzee" Croshaw makes in his review of the game, I'm guessing what occurs along the lines of option 3. However, that's just a guess. What actually happens when you select 'Continue' after completing Bastion but before starting a new game?