Arya

[Lord Lyman]

Where in the show did they ever mention "The dragon must have three heads"? I thought that was what book Dany heard when she went to the "House of the Undying". Show Dany never saw that and I don't recall it ever coming up.

[Lord Varys]

8 hours ago, lomiller said:

The model for the 3 heads is Aegon and his 2 sisters/wives.  Dany is pretty clearly linked to Jon romantically making 2 of the 3 heads.  We've also reason to believe that GRRM's original intention was to link Jon and Arya romantically, and even if the romance is dropped the emotional linkage has been played up at every turn.  There is also a strong symmetry to it, Arya being a Stark and linked to ice, Dany being Targaryan and linked to fire Jon being both. 

Arya is not a dragon. She is not the head of a dragon, either. The three dragon heads will ride dragons, not (only) marry Targaryens.

[Wik]

9 hours ago, Lord Godric said:

You're ignoring the point that there is no Night King in the books. Therefore no one in the books is going to be the one to kill the Night King. 

I agree with you and realize this now.....BUT I guess the over arching point is: We know the Others and WWs are supposed to be the REAL threat and they sure as shit exist. So, there will still be sequence where Jon and many other characters are fighting them. While I like where Arya has gone, I think Jon's story arc, clearly, is based on these events more so than the "game of thrones" plots hatched in King's Landing. 

So, from that standpoint, I see (and also feel the same way) where people are coming from....can Arya HELP Jon is his fight with the WWs and Others? Absolutely! But she isn't "the missing key" in the fight against them.