HP Fans: Question about Ex-Death Eaters? (Or however you say it...)?

Okay, maybe a few of you know that I'm writing a fan-fiction about Dramione. (Draco+Hermione) My question is, do past/ex-death eaters still have their Dark Mark on their left arm? Does it stay there forever? Even if they stop supporting Voldemort? Because, in my fan-fiction I need proof that Draco has stopped supporting him. I thought of Draco unrolling his left sleeve and showing Hermione that his Death Mark is almost invisible...But I doubt that their Death Mark ever goes away.