You only have yourself to blame for this.
The game hands you a pop up on a silver platter to warn you that it's the point of no return.
If you did not heed it's warning then all you can do is muster up and start a new character.
Besides, the game has 4 paths, each path which can produce other endings as well.
It would be a waste to not play through the games full content.
So start a new character, be an explosives legionnaire who refuses to take off his/her armor.
Should serve as an interesting playthrough.
(I just don't see the point in buying a game about replayability if you're not gonna use it. Would be like buying L4D and only playing through the campaigns once. It's meant to be played over and over until you get sick of it.
)