Please note that this is the walkthrough for the final level of Spec Ops: The Line, and as such, it contains very heavy spoilers for the ending of the game. If you do not wish for the end of the game to be spoiled, DO NOT read on.
Hurt and alone, Walker will wander into Konrad's tower in search of a final confrontation. No enemies will await him in the lounge. Walk slowly up the red carpet and ascend the lavish staircase ahead. As you reach the top, you will see the 33rd in the room ahead, but they won't turn a gun towards you. Instead, they will reveal that they are all that is left of the Damned 33rd, and they will surrender themselves completely to you. With a salute, they will usher you into the elevator. Climb inside of the elevator and ride it all the way to the top floor.
When the elevator ride ends, leave its confines and walk out into the darkened room ahead. Konrad will question Walker about the mission as you move about through the various rooms of the home. No special items or Intel will be located in this room, so simply head up the stairs on the right and move forward to meet Konrad. He will be painting a version of the grisly scene that awaited you when you used the white phosphorus when you arrive. As he asks Walker's opinion of the piece, Walker will become angered and blame the whole thing on Konrad. Konrad, on the other hand, will turn the blame back onto you. You are, after all, the one who pulled the trigger on the white phosphorus mortar. With this accusation, he will fade behind the painting and control will return to you.
Go around the large painting and approach the chair by the window. You will find Konrad, dead in the chair with a gun in his hand. As it turns out, Konrad didn't survive the storm and the failed escape after all. You were never meant to go find Konrad like this. Instead, you and your squad marched deeper and deeper into the city, pressing ever-closer to Konrad and killing more and more people in the process. With this final speech, you will be left with one more choice. You can either kill "Konrad," or you can let him finish his countdown to five. When he reaches five, he will kill you. You may now choose to atone for your sins by dying, or to live through the twisted revenge fantasy by killing your hallucination of Konrad.