The Ending

I found the ending of WE interesting.  It ended a lot different than I thought it would.  I figured in the end with D-503 being free and with I-330 or O-90.  Instead he had the Operation and returned to being a "machine" of the One State.  He also turned in I-330 as being part of the group trying to destroy happiness.  I believe that D-503 wanted to be a good citizen all along and that he was just dreaming about corruption.  Without the structure of the One State, I feel as if D-503 will fall apart.  I still am left wondering what happened to O-90 in the end.  Did she actually escape or was she caught and D-503 just thinks that she got away?  This ending kind of left it up to the reader to decide the final outcomes for some of the characters.