I'm currently playing through this game (bit late to it, I know) and am wondering if the game will allow me to go back to previous regions and find all the collectables (Riddler Trophies, etc) after I've completed the story - or if I need to do these as I go through the game?
The game does not continue, it ends immediately after the last boss fight; however you can roam around as you please just before it begins.
Spoiler about how you know you're about to reach the no-turning-back point:
When there are about 20 goons clapping and cheering for you just before the visitor's center. Once you open the door to the visitor's center, you cannot go back.
If I recall correctly there's also an auto-save just before the no-turning-back point so after finishing the game you can load it (also via "continue") and play from there - but it takes place before the final fight, so it's not a continuation.