I keep hearing that and to be fair, I don't see book Dany going mad either ,unless you do pull that subversion out of nothing. Jon, who was betrayed by his own people have more motivation to go bitter and become insanely paranoid like his grandpa Aerys. Aerys' madness increased after he was kept a hostage for some considerable time.
Dany is going through worse than being held hostage. Last I checked, she had diarrhea in the wild. Not to mention pulling subversions out of nothing is GRRM's trademark at this point.
There is one thing about readers is that they claim that Dany can become mad because she's a Targaryen, forgetting that Jon is too, and he also has outbursts of violence that Dany hasn't yet had. Whenever she's acted violently, it's based on being provoked, like how she crucified slavers who first crucified children out of spite for her.
Dany is pure Targaryen, not half, which Jon is. Remember, his mother was a Stark. That, and Jon grew up with a positive male role model in Ned, and a loving brother in Robb. Catelyn was a piece of shit to him, but she was the exception that proved the rule. Ser Roderick, Arya, Robb, Ned, they were all nice to him.
Dany, on the other hand, grew up with Viserys as her only guide, and he was a vain-glorious twat who had dreams of revenge, conquest, and power. Put Jon in the same situation Dany was in, and the worst he'd do is decapitate the slavers and put their heads on spikes outside the city as a warning. He wouldn't crucify them, because that is not what Ned would've done. Neither would burning the capital. But Dany might do it if the capital put up enough resistance against her.
And the one who's burning the capital to the sound of bells is Connington. It's as foreshadowed in book 5 as when Dany saw a man with a wolf head in her visions and we had that in book 3.
We don't know that for sure. What we do know is that GRRM gave an outline of his ending to Dan and Dave, and Season 8 was the result.
For all we know, it could be Euron who burns the capital after using a dragonbinder horn to steal a dragon from Dany. Burning a capital city with a dragon is right up a pirate's alley, especially if it's a pirate with apocalyptic visions. Or maybe, he's just a nut, and he can't actually steal dragons with that horn.
There is no leader of the Others in the book, though. At least, not for now and I honestly can't remember if GRRM said we wouldn't have one. He has a more chaotic view of magic, so I'm assuming the Others are walking South for a different motivation than being sent by their leader.
But that's the thing; we don't know shit about the Others because all we had was GRRM focusing on human soap opera drama and backstabbing for 5 books. For all we know, they could have some leader who serves as a universal off switch for the undead if he's killed. Or maybe there is some sort of hive mind and you have to kill every last member of the Others to turn off the undead army. But most of the cast don't give a crap about them because they've been sideshow freaks for five fucking books. If a random conjurer somehow killed the Others, the setting would barely change.
I'm willing to bet that whatever kills the Others has something to do with Arya. Unlike Jon, she's a full-blooded Stark, and the only true born Stark at this point with some fighting capacity. After all, the undead are a Stark problem; the rest of the kingdoms barely gave a shit about them.