I could be wrong but in my mind this woman is more guilty than Dan. She's the one that put it all together and presented it to Dan and he was the idiot that bought it. His own Ego and Hate for Bush did him in. She has to go no matter what.
You are not wrong. On TV magazine shows, the producers are the ones who do 90% of the work. This was Mapes's baby from start to finish; Dan would never even have heard of the "memos" if it weren't for her.
If this were an episode of "Law & Order," Dan would be the accessory who gets immunity about 20 minutes into the show in exchange for his testimony, while Mapes would be the master criminal, fighting and screaming for the rest of the hour until she finally gets convicted and sent off for 25 to life.
Well, assuming Dan would ever admit to having done anything wrong in the first place, anyway.