The NK walked through dragon fire last season and it just retreated around him. Unless they are planning to have Drogon bite him into tiny pieces or sit on him it wont work. Even if it would work, the dragon fire would roast every living person and thing in the grove. Bran and everyone would be dead. And projectile weapons would work better in a restricted tunnel or hallway because the NK would have less space to move in i.e. shooting fish in a barrel. The grove makes no sense as a trap unless Bran's planning to use the weirwood magic.
That fire was from the burning corpses of wights. He did not take a shot directly from a dragon, a source of magic in itself, and I think that might make a difference. Perhaps we'll find out whether it does or not in a few days.
And I disagree, tactically-speaking. Look at a map of Winterfell. Multiple archers and spearmen on the walls surrounding the Godswood would have an excellent chance of nailing him from every side
-including his exposed rear- as he swoops in.
I wouldn't anticipate the NK entering inside the fortress all alone just to mindlessly get at Bran. If Bran was inside, the NK would use Viserion to force openings in their lines, incinerate the gates, and enter later with his troops in the van. Isn't that basically what happened when the 3ER lair was sacked back in Season 6 "The Door"?
As for the potential blast radius from dragonfire... well, as I said, I think the plan is terrible for this and other reasons. The Dragon breath weapons will have to be employed before he gets too close to Bran and his Ironborn bodyguards --surely that's what Jon is thinking.
I agree that it's not going to work, Winterfell will be lost, and I think that they'll have to make Lightbringer to take out the NK later.
Using Bran as bait with his limited mobility and no big Hodor around to haul him out when the plan goes awry is another issue. Maybe Bran will be slain but will be warged into someone or something else (like one of the dragons) before he dies so that the 3ER can still continue its existence in one form or another.