Technically speaking, the fight is Daenerys vs Gandalf, so if Danny dies, the fight is over. I think.
GoT dragons are just animals, so I'm pretty sure the dragons need Danny to steer or direct them. Are the dragons "equipment" that Danny has to be able to use, or are they bloodlusted like her? Meaning, if Danny dies, does Dragon continue the fight, or does he screech and fly away?
Anyway, if Danny is the key—if that's correct—Gandalf only has to Jedi-TK and knock Danny off the dragon.
So, fight begins, maybe Danny takes to the sky (her standard tactic, so I think yes, it happens) while Gandalf raises the same kind of force-bubble he used to defend against the Balrog. Then Gandalf just Jedi's her off the dragon, she falls, she dies, bell rings, fight's over, victory: Gandalf.
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Gandalf's shield took that hit. I don't think it unreasonable to suppose he can deflect dragon fire in the same fashion.