Once you return to Milly, you have several options. If you tell Milly that Bill is dead, or lie and say he is alive, she will hand over six stimpaks. If you complete a Speech check, you can convince her that you saw and heard him being torn apart by the trogs, so you had to put him out of his misery, and Milly reacts to this news by fainting. She drops the stimpaks as she would have given you upon fainting. However, it is likely for the ragdoll to spin around, flinging the stimpaks out of sight, so saving beforehand is advisable.
You cannot engage Milly in dialogue after the speech, but before you sign up to fight in the arena.
Be careful when looting Wild Bill's body, as it is possible to be attacked by a nearby trog. It can come from the staircase to the right of Wild Bill's body.
If you choose to help Ashur quell the riots and maintain control of the Pitt before telling Milly of Bill's fate, the quest will not be able to be completed, as Milly will no longer engage the Lone Wanderer in conversation, since you sold them out.