since this show is going on for 15 seasons which is practically unheard of for a sci fi show, the last time i heard such a thing was xfiles, not even smallville with its rich superman mythology got 15 seasons. But I think by the end of that final episode, there shouldnt be any unanswered questions, yes there will be the obvious what happens next, even if sam, dean, cass and jack go to heaven, we will ask what happens next for them, what will they do in their free time for eternity now that they arent hunting? And some things are just more like fan demands more than great opportunities, like seeing the leviathans take on eve, that is more of a fan demand rather than a missed opportunity. The final thing to keep in mind is even with 15 seasons, they cant please every single fan demand, not with only 20 episodes left, its impossible, we dont know what every fan of supernatural wants.
i would say for me im going to be dissapointed if:
the shedim dont appear, even if they are evil and only setup to be wasted by the winchesters, at least bring them in, people can tell me they arent needed but i still disagree, the shedim were most likely the angels that rebelled with lucifer and fell from heaven and they are pure demons, not ghosts who turn into black smoke, i think a pure demon is something we could gain from
id like closure between dean and jack, i dont think these two ever had a true respect from one another, or at least from dean to jack, not until the time came to kill him
id like the last 20 episodes to be as action packed as possible with as many old characters used well as possible, i dont care to see lets say azazeal just be brought back to die by dean again, like let him fight cass or sam or someone else, just examples like that, and the series finale, even if its 1 hour like the other finales, make it action packed too, i know, fighting chuck is going to look incredibly phony, the most phony fight they've come across cause he is god, he can wish them away so the fact he would get into a fist fight with the winchesters will look incredibly silly but there needs to be an action piece in it, spn is not just about talking out family problems, any fan new or old should know this
id like to see bobby back, the real one that is, id like him to get closure with rufus and see what they had going on in omaha, basically any unanswered question, i dont want any question set up not to get answered, they dont have that many questions that need to be for one, secondly its 15 seasons, there is no good excuse to why they cant be answered in some fashion. I think for me id like to know why billie lied to dean about michael, that bothered me especially knowing that jack blew up the malach box.
i think there needs to be closure with lucifer and as mark pellegrino, he is by far one of the best characters in the show and the series best villian imo, not cause he is the devil but because he is so entertaining to watch, i dont think they need to make lucifer the villian yet again and go with the trope of using the devil as the final boss, but he can return and maybe help the boys out, i dont think he will ever respect the winchesters and vica versa however i could see an understanding of maybe he realized what a horrible father he was to jack and wants to right it by not becoming like his dad. Oh a few more things, bring gabriel back cause his death was a trick too i think and give adam more closure, maybe they can apologize for not getting him out of the cage when they had the chance. Id like to see michael too while inside of adam but i just hope michael isnt used as the villian, we just had that and look how it turned out. And bring back dark kaia too to get her spear which is now destroyed, basically any character who doesnt have closure yet, bring them back.
i think that is it, with the news that jeffrey morgan and mark sheppard wont return, i cant be too upset, that isnt the writers faults, even if they did something to provoke the actors, the actors chose to walk away, i think bringing back john is more of a creative decision, mark straight up doesnt want to play crowley anymore