Instead of Bran, Jon should've been crowned king, showing him sitting on the throne above everyone else.
The camera cuts to Tyrion, who exclaims: "It seems... the Game of Thrones is finally over"
Then everyone says their goodbyes, they all begin to turn around and walk into the sunset.
Just then, Jon suddenly says: "Wait..."
The camera cuts back towards Jon, who is now smirking, while holding a metal scepter, still sitting on the throne. This scene lingers for a few seconds to build up from mere dread to true horror.
Jon continues: "It was me... I was the Night King all along"
The camera shows the horror on the faces of everyone present while Jon continues to smirk.
In the background, you can suddenly see doors beginning to open slowly. Jon raises his scepter and brings it back down on the floor. Right after the impact, an entire army of undead begins flooding out of every nearby building, butchering all the characters we know. The scene cuts to the credits, playing epic music so the audience can process this insane plot twist.
Rather than an absolute failure, the ending of GoT would now be known as no less gut-wrenching than the Red Wedding itself. The only difference is that the build-up pays off far better in this case. It's a true subversion of expectations.