Great episode. And really creepy too, especially Pinkie's turning scene, holy crap! And this is a show aimed at little girls!
My prediction of how everything will be resolved: The gang defeat Discord, but instead of being encased in stone again, Celestia and Discord come to an agreement whereby Discord is given the Everfree Forest to rule and we learn a valuable lesson about how the world needs both order (Celestia's Solar Empire) and chaos (the Everfree Forest ruled by Discord). This would be in line with the show's theme of friendship and it would also allow Discord to return in future episodes.
My prediction of how everything will be resolved: The gang defeat Discord, but instead of being encased in stone again, Celestia and Discord come to an agreement whereby Discord is given the Everfree Forest to rule and we learn a valuable lesson about how the world needs both order (Celestia's Solar Empire) and chaos (the Everfree Forest ruled by Discord). This would be in line with the show's theme of friendship and it would also allow Discord to return in future episodes.