Cersei and Qyburn said they had a weapon to defeat Daenerys' dragons, and after Bronn finally used that secret tool, is Drogon OK on Game of Thrones? That huge arrow injured him badly enough for him to have to make a quick landing, but not so much that he fell to the ground without any control. He was also alive enough to shoot out that mouthful of fire at Jaime, so he just might pull through.
And it should also be noted that a few seasons ago in Meereen, Drogon was injured enough to take a long nap after that particular huge battle, so he's already been through some stuff. When Daenerys was cornered in Meereen and Drogon swooped in to save her, he was also speared several times. But even then, before he'd grown to be the insanely gargantuan monster he is right now, he wasn't permanently injured. Instead, he flew away with Daenerys on his back, only to stop and rest miles away.
Since he's the biggest and toughest of her dragons, Drogon will probably be OK on Game of Thrones, especially since literally no one would have forgiven Bronn for killing Daenerys' dragon. Besides, the other two still haven't let the Mother of Dragons actually ride them, so how is she going to continue to intimidate her enemies if she doesn't have Drogon?
In the preview for Season 7 Episode 5, you can see Drogon multiple times. First, as Daenerys urged the remaining Lannister and Tarly soldiers to basically join her or die, and then as Drogon screams in Jon's face. Even though Cersei's weapon against dragons probably should have killed him, Bronn's shot at Drogon's face wasn't enough to do him in, and now the machine is reduced to ashes. So unless Qyburn has another one stashed away somewhere, they're going to have to think of another way to kill Daenerys' "children."
Just like in Meereen, Drogon's injuries on Game of Thrones Sunday night were minimal in the grand scheme of things. He might be down for a little while, but he's also the biggest dragon currently living, and he's already survived battle wounds.
Of course the fact that the Lannisters were able to hurt Drogon at all is kind of scary, especially in light of what we know about the wars to come. As Qyburn told Cersei earlier this season, "If they can be wounded, they can be killed," so even though Drogon is OK right now, the fact that they got a shot at him at all is a sign — or omen? — that he is not invincible.