I consider the short and clear ending more convenient, even so, you can add an option (in the menu or at the end of the game) to continue, infinite challenges / skills or something like that.
I consider that each character has a different objective in the last mission, but that in some way they connect with that of the other characters, in this way they will all escape at the same time.
Or each one will have a different ending ?????
With the objective you mentioned, you can even connect them, by obtaining an object that serves for a task of the last level (not used at some point).
I have some doubt, but I don't know how to explain, so I'll wait until the update to see if it persists.