Well, this is the episode of Game of Thrones we've been waiting for — or at least, one of the episodes. In 7.4, we finally get to see one of the fearsome fire spewing dragons in battle... against Jaime Lannister's army.
Except it's more than just an army, modeled in fantasy retrospect after the Romans, wearing red and all. But just as the Romans and even more so their Byzantine successors were known for their ingenuous weapons, the Lannisters have on their side the dragon-slaying auto-spear we've seen in development this season.
It's never been used before. It's powerful, but is it enough to bring down a dragon? Well, it depends where it hits. And after missing the first time, it indeed hits — but not in the head. Our dragon, with Daenerys astride, is wounded, brought down, but still more than able to fire its fire.
Jaime makes a desperate, heroic attempt to kill it, but a man on horse with a spear is not as potent as the mechanized spear machine, and Jamie doesn't get close enough. His charge is refuted by dragon fire. We see Jaime floating under water in the last scene. Is he dead? I don't know — I haven't read the novels, and I've seen no spoiler. But if I had to bet, I'd bet on his surviving.
But we and Cersei have learned something very important — the dragons are not invincible. They can be slowed down and stopped, and likely even killed. Just as the Romans were stopped in the end, as well as the Mongols — stand-ins for the Dothraki in this timeless fantasy drama — so the dragons, like all living things, can be stopped, too.
Which leaves us with the dead of the way north. They'll be the hardest of all to stop, seeing as how they're no longer alive. At this point, only Bran may be privy to their ultimate fate.