Alright, I've played Skyrim for well over 85+ hours now and the game is fantastic, I've 6 achievements away from maxing the game but I've ran across a problem in the game. I want to get the Ring of Namira, but I killed Eola because I choose the wrong option in the dialogue, so is it possible for me to still get the achievement or be able to get the artifact?

Another common problem is the Markarth guard glitch which is making it impossible to do any thieves guild quests.

I can't go back a save because before these problems I was around level 24 now I'm level 46.

BUMP

I have the same problem, I killed Eola by mistake 100 game hours ago (she was stuck), and now I have all the trophies except the Daedraedtic one;
Please insert a way to reset the quest!

Information from wikia,see if any matches with your guys problem:

• It is possible, that if you choose to kill Eola in the Markarth Hall of the Dead, Brother Verulus may become glitched and will continually approach the player for conversation whenever the player enters the keep.
  
• If you kill Eola after she asks you to lure Brother Verulus to the cave, you will still be able to ask the cannibalistic citizens about the feast.
  
• Occasionally after killing Verulus while he is sleeping, he will phase through the table and it will be impossible to feast on him. Saving the game and reloading will fix this.
  
• If the cave has been cleared out before the quest, entering the cave will result in a game freeze.

• If you kill Eola within Reachcliff Cave after you have accepted -Convince Verulus to follow you- some citizens of Markarth will speak to you as if you are a member of their cannibal cult. Even though you have not lured Brother Verulus to be eaten or taken part in the feast.
  
• Sometimes when Eola comes up to you in the hall of the Dead and starts talking to you, the disembodied voice will keep on talking over her, making it difficult to understand what she is saying.
  
• After you bribe Brother Verulus to follow you, he may not and the quest will be uncompletable, and by that time, he will be unkillable.
  
• If you kill Eola just as you enter the cave, as in the notes above, the shopkeepers will not be hostile yet dialouge options will appear "You were at Namira's feast, weren't you?". There was no feast since she lays dead at the entrance. The quest marks as failed this way.
  
• After you bribe Brother Verulus to follow you, the game may lead you to "Namira's Shrine" as the next quest objective instead of Reachcliff Cave which may be a typo. (XBOX/PC version)
  
• (PS3/XBOX) If you elect to kill Eola the first time she is encountered in the Hall of the Dead, Brother Verulus may glitch, never leave Understone Keep, and constantly stop the player for conversation while he is in the keep.
  
• If you kill Lisbet before returning her statue of Dibella, it will be impossible to drop. This quest can never be completed.

You cant.
You can however start a new game.
But why people find these silly 'achievements' even worthwhile Ill never know.
It has nothing to do with the game at all, just something slapped on.
You havent completed the game by a long shot if you have all these 'achievements'.

It feels nice to have achieved something i guess Even if it is, uh, worthless.

Like someone else said, you can look at them as another quest. A really really long quest.

achievements are only there for developers to data mine peoples playing habits.