^ Concerning the finale, a few months ago I wrote a fanfic about how it could all end.
Cas finally gets sick of the fact that angels aren't the fearsome warriors they used to be (this was before we found out they were endangered), and gets fired up about restoring Heaven--and for that, angels need their wings back, which means getting serious about deciding to tackle reversing Metatron's spell for real.
Sam and Dean dig up a piece of lore that tells them how (big surprise: Crowley lied back in season 9; the spell they're using isn't specifically a spell to restore Heaven, but rather a way for whoever uses it to influence reality). Lucifer is also back (this was before the season 13 finale so don't hold it against me) and when he hears about it, he decides to try to stop them (so he can do it instead). The brothers return to Sioux Falls and dig up something from Bobby's salvage yard (where Cas has to help defend them against a horde of , one ingredient that's needed; they lean on Crowley (again, pre-season 13 finale) for the second, and to get the third, they enlist Rowena's help to spring Michael from the Cage (a scene I'd love to see them actually do: Lucifer tries to pull a "sympathy for the devil" like he did in season 5, but Michael isn't fooled and knocks him back telekinetically before healing the wounds Adam suffered in the Cage, with the same flourish Lucifer did in "Mamma Mia").
They set everything up in the power station above the bunker, but Lucifer and basically every demon in Hell attack before they can. Lucifer kills Rowena, Cas smites demons that aren't in meatsuits, and the brothers do badass Winchester stuff, but it's not enough--even Michael is nearly overwhelmed, but while Lucifer's back is turned, manages to jump-start the spell with a blast of archangel power (the ingredient: "Heaven's brightest light"). A blast of light shoots into the sky, the demons vanish, and time freezes as Chuck appears.
The spell they used? Not about influencing reality at all. It was the divine equivalent of a signal flare, to let Chuck know when everyone He left on earth had found a way to put aside their differences and work together (angels, demons, and humans). Beaming with pride at their achievement, he doesn't restore Rowena (same reason as Cas didn't interfere with Mary's death this week, she's happier in Heaven), but he does offer Crowley an upgrade, restoring his soul and granting him admittance to Heaven. Then he turns to Lucifer, and asks for his help in putting their fractured family back together. With one last sneer at the Winchesters, Lucifer agrees and returns to Heaven. Then he snaps his fingers and restores the wings of every angel in creation, which has the secondary effect of freeing all the trapped souls from the Veil--the clouds part and create a false dawn as all those sparks of light rise up from the Earth and make for Heaven--and the restored angels almost immediately start teleporting into the room to see their father. Finally, for his selfless service and unending faith, Chuck makes Castiel an archangel, and tells him his most important job is about to begin (but we don't find out what it is). To the Winchesters, he gives a speech similar to the one Cas gave Dean at the end of Swan Song--an assurance that they're doing the Lord's work, and that when they pass on, no matter what any reaper says (again, before Billie became Death), they have a place in Heaven and will be reunited with their loved ones.
With that, and a burst of light, everyone except the Winchesters (Cas too) vanish. Cas says his goodbyes--promising to answer their prayers anytime he can--and departs for Heaven. The last shot is Dean locking up the bunker as he and Sam get into Baby and go out on another hunt, and then drive off into the Lebanon sunset.
