Paidion,
I meant that satan played a part in causing Adam and Eve to sin. He fits into the story and continues to do the same thing that He did then and that’s to find ways to get people to sin. I think how one views free-will affects our view of whether the devil and the demons will be saved or not. I believe there is only the illusion of free-will. Satan helps play the part of the bad-side in the choices we think we make with free-will. In order for there to be sin no longer, there can be no tempter anymore. Thus, the devil and demons must be removed from the picture somehow.
Addendum: People are a product of their circumstances and past. It is Christians who live in the future and continually live in the expectation of sanctification. As a result, Christians become different from regular people (sinners) in that they are dependent on Christ for everyday living. The devil is the one who reminds us Christians of our past life before we were saved. That was always his mission (and that’s why we should remind him of his future). When I say that I don’t know what his purpose would be at the end of the reconciliation of all things, I mean that there literally is no more sin to be endured and therefore satan would be consumed by the judgement of God because his mission ends. Humans are variable, though, unlike satan. If satan somehow did make it then he would have to 100% different being. Whereas the most sinful sinner that has ever lived would still get to retain .00001% (or some arbitrary percentage above 0%) of their personality.
This is the part I would dare say that satan is not even deserving of “personship”. He is a bit more like a robot programmed to be perfectly evil and to tempt all humans to sin but not past what they are able. What see throughout the account of faithful people in the Bible is not so much about believer versus Satan but rather believer versus sin in self. It’s about maturity, not a conflict between God and satan. While satan is often blamed for evil in the world, the responsibility of it really falls on God’s shoulders.
In response to the potential purpose of satan “glorifying God’s ability to save the most evil of the creatures He has created” if he were saved, I don’t really understand what that means. Sure, satan is a creature of god. What I don’t understand is why God would need the praise from the mouth of satan when He can get it all the praise of angels and good humans. He doesn’t need satan and the demons. He doesn’t need us either. The difference is that Bible clearly mentions that God wants us saved where it makes no mention of wanting satan saved. In fact, I’m convinced from the language in the Book of Revelation that God positively wants satan and the demons destroyed.
As for the difficulty of accepting God creating things so that they would ultimately be destroyed, there is no need to accept it emotionally. The Bible doesn’t really get into the details of how satan and the demons will be destroyed. This implies that is not something that Christians need to worry about. There are some things we should just not question God on and let Him do what He needs to do. This is sort of what I meant when I opened my previous response with “God is sovereign”. I don’t play philosophical games with God’s sovereignty. 
