I just want to write it down so that I can say "I told you so" should it actually happen. Putting it under a cut, though, because I'm not sure anyone wants to read or even accidentially glimps how I think the show might progress
They are going to do Camlann. They are going to kill Arthur and Merlin will be unable to prevent it. But they'll do it around episode ten or even earlier. Then they will go on to Avalon and the wait for the "Return of the King", integrating that part of the of the legend as well. Maybe they'll even go as far as redeeming Morgana. I so want that, and I think it's possible, the way they made her so good and righteous in the beginning, being almost relunctantly turned "evil" by fear, then kind of playing at being a villain (my take on series 3), and finally the as yet untold horrors that must have happened to her and Aithusa. I would so love if they had her have something to do with guarding Arthur after his "death", maybe realizing that she loved her little brother all along (I'm sticking with her being the older of the two). That would be so awesome. So: Arthur dies, but his "rebirth" and "return" will be an integrative part of the show, mabey even the end.
I wouldn't put it past the show to play with the entire legend like that. There is this thing about "breaking the neverending circle of his fate", and I read that as a kind of meta reference to all the Arthurian tales that came before and that more often than not end with Mordred's betrayal and Arthur's death. Some people might disagree, but I think the show has been marvelously witty referencing previous retellings of the legend, starting with Geoffrey the librarian and the various episode titels that quote different Arthurian books (I was still too lazy to research if actually all of them do, but I recognized a whole bunch). I even liked what they did with Lancelot and Guinevere, although I might be the only person out there who did. And I remember already hoping after series four that they would include Camlann and Arthur sleeping in Avalon and Morgana being redeemed. I would so love that.
I don't know how the magic reveal would fit into that scenario. I honestly don't care all that much, but I'm sure there would be a couple of ways to include it and make it epic. Maybe it's the reason Merlin isn't there to prevent Arthur "dying".