This case has really intrigued me ever since I saw the "Vanishing" documentary. From reading up on this case, I've come to a bit of a conclusion.
Personally, I think it's possible that Maddy got in a car with someone she knew and things turned ugly. This would help explain why LE has interviewed and cleared the partygoers - Maddy probably didn't leave the party in a struggle. She probably got in a car with someone she knew, therefore she seemed normal. I think it is very possible that none of the partygoers saw anything suspicious or even saw Maddy leave.
Her friend had stated on her Facebook page that she told Maddy she was leaving the party and said she could come with, but Maddy said she didn't want to leave her truck or belongings behind so she decided to stay. I think Maddy eventually wanted to leave the party since she was kind of alone (her friend stated that people at the party were more like acquaintances than good friends) so she asked someone she knew to either pick her up or come to the party and drive her home in her truck. With the latter, she could eliminate the concern of leaving her truck behind.
The reason I think someone may have driven her truck with her in it is because LE/her parents/her friend found her purse still in the truck. Maddy's belongings were still at the campsite, including her rings, so robbery was not a motive -- this also suggests the crime was more personal, potentially someone she would trust driving her truck or at least getting into a car with. I think the person knew the rings would identify her so they drove back to the lake with her truck, parked it in the same spot, put the rings outside the tent, and left. That way, it looked like Maddy never left the party.
The only confusing part about this theory is the tent. If Maddy had packed her tent up with the intention of going home, I think it's possible her kidnapper set her tent back up with the intention of making it look like she never left the party. Sounds a little crazy, but it's a small thing to do if you're trying to cover your tracks.
Another note about the rings -- I don't think she took them off herself as a sign that something was wrong because it seems a bit odd that if she was leaving in a struggle that she would have the time to do that (how many rings was she wearing? How tight were they on her fingers? How long would it have taken her to remove them?). Also, why would she drop them at the campsite where people would obviously be looking regardless if her rings were there or not? Why not leave a trail?
Furthermore, it sounds like the rings may not have been there until Sunday because that's when they were found:
Maddy's friend's facebook page said:
It was SUNDAY that I went looking for her with the RCMP, searchers, family, and everyone that was looking for her that I found the RINGS and gave them to Maddy's Mom. 48 HOURS makes it look like I found all of that the next day! If I had I would have gone straight to the Police.
She went to the campsite on Saturday looking for Maddy. She called her, looked at/inside her tent (she mentioned it looked "messed up" inside the tent on 48 Hours), but nothing alarmed her or made her think anything was wrong. Then on Sunday she went back again and found Maddy's rings outside her tent. Were they there on Saturday and the friend just missed them? Or did they show up on Sunday, indicating someone placed them there?