If you are at the end and have defeated Legate you cannot leave without facing the NRC general which triggers a cut scene that leads to finish. I have received the pip boy message for HH but cannot travel out of camp. Do I have to go back to a save that is before the point of no return??

Was the warning popup message right before the point of no return at the dam battle too subtle or something? :facepalm:

Less subtle then your reply.

Yes, you will have to go back to just before the final battle in order to do Honest Hearts on that character. Note that this will apply for all subsequent DLCs as well.

Once you start the final battle, you can do nothing else but complete it and end the game. You can't start any DLC after you get and accept the message that you are at the point of no return.

Sorry friend, but it looks like unless you have a save from before that point of no return you will have to start a new character.