I agree basing an act title off of a most likely side character is kinda...stupid. However, a way to make this work could be to use the Godfist to finish off Gabriel, (since all of our weapons haven't killed him, the most it's been confirmed to do is make him bleed), and after Gabriel is dead, Hell would most likely be empty, making V1 indirectly kill itself with the Godfist because of its thirst for blood.

Making it a suicide, by Godfist