I am currently through my first game play of Dark Souls
After retrieving the Lordvessel from Gwynevere, Princess of Sunlight , i warpped out to Daughter of Chaos Bonfire to fight CEASELESS DISCHARGE.
And as you have guessed I attacked the firekeeper Quelaan out of the blues and later realized the sin; She is dead and the Bonfire is down.
(Not my image though)
What will this sin has affect on my game play beside from not being able to unlock advanced pyromancy?
Can I revive the Bonfire?
Best Answer
No, once a fire keeper is dead, there is no way to revive the associated bonfire. Killing npc's adds to your overall sin level, which determines how easy it is to be invaded, and opens you up to blue invaders as well.
You can visit the pardoner just after the Gargoyles boss fight to remove your sin level at the cost of souls.
Other fire keepers to watch out for (so you don't accidentally kill them):
EDIT: When you enter New Game+, all npc's you have previously killed will be revived, and your sin level will also reset, so it's a good idea to kill all the npc's for special items they drop and souls before fighting the final boss.