All That Remains is a Main Plot quest in Dragon Age II during Act 2 revolving around the disappearance of Hawke's mother, Leandra.
Acquisition
- Complete Prime Suspect and Offered and Lost.
Walkthrough
You can optionally report Leandra's disappearance to Moira in the Gallows, though doing so has no lasting effect.
There are two ways to get access to the Dark Foundry:
- If Gascard is alive, you can find him in Darktown. Tell him to perform the ritual. Perhaps reflecting the gravity of the situation, Fenris and Anders will let this one instance of blood magic pass without comment or consequence. Sebastian, however, still disapproves
Sebastian: rivalry (+5). If you turn down Gascard's offer to use blood magic, Sebastian approves of your decision Sebastian: friendship (+5) and Merrill disaproves Merrill: rivalry (+10) . It is still possible to accept Gascard's offer after turning him down. After the instant transition to the Dark Foundry, Gascard will accompany your party through the area.
- Certain dialogue choices may result in Gascard's death at your hands or execution by the Templars, rendering this option unavailable. If you cannot find Gascard in Darktown, speak to Moira in the Gallows and she will reveal that DuPuis was executed. Gamlen then becomes your only aid.
- An alternative solution (and the only available path if Gascard was killed during Prime Suspect) is to meet Gamlen in Lowtown at night. Speak to the Urchin and either pay or intimidate him Varric: rivalry (+5) to obtain information. Then follow the blood trail to the Dark Foundry entrance.
Result
If Gascard DuPuis is with you in the Killer's Lair for the meeting with Quentin, there are three possible outcomes:
- If Varric is in your party, he has a very interesting reaction. Youtube Spoiler [1]
- Without Varric you can persuade Gascard to turn away from his current path via a diplomacy (Diplomatic personality only) option. If successful he will fight alongside you in the battle with Quentin. There is also a star option that becomes available with an aggressive personality that will convince Gascard to help you.
- If Gascard feels disinclined to assist Hawke, he will join Quentin for the final battle.
Unlocks Following the Qun and The Captain's Condolences companion quests.
- The Gloves of the Overseer, Gloves of Enasalin, or Stonehammer Gauntlets are in a chest in the killer's lair, before the final encounter, depending on Hawke's class.
- If a companion was romanced, they will come to console you in your bedroom at the Estate. (This happens after the conversation with Gamlen) If no companions are romanced, Aveline will come saying she has heard the news and that you know where to find her.
- In the Lair there is a letter to the killer from someone in the Circle of Magi, congratulating him on his discoveries and indicating that the writer has placed certain books on magic in a drop-off place for Quentin to obtain. The letter is signed "O." The identity of "O" may be revealed to be Orsino himself during the final quest of Act 3 if the player sides with Meredith.
- No matter which option you choose above (with Gascard's help or without), there is no way to save your mother from her unfortunate fate.
Isabela: rivalry (+10), if you kill him 
Isabela: friendship (+10).Note
If you are seeking the Supplier achievement, be sure to grab the Orichalcum in the Killer's Lair.
If you bring both Aveline and Fenris, Aveline will take precedence for interrogating Gascard.
Gallery
Alessa found dead
Leandra walking towards Hawke
Close-up of Leandra dying in Hawke's arms