Broken Steel Fawkes is one of three companions that can be sent into the irradiated chamber in the Jefferson Memorial to activate the purifier during Take it Back!, along with Charon and Sergeant RL-3. His response to agree or refuse depends on if Broken Steel is[11] or is not[12] installed.
If Broken Steel is installed and Fawkes is an active companion during Take It Back! and is sent to start the purifier, he is referred to as a hero in the epilogue, then when the game resumes, Fawkes will be waiting in the infirmary at the Citadel.
Fallout wikia says
Allright, it was a while since I played it, sorry about that!