Dead badasses? Syrio Forel. Former first sword of Braavos and both wise and exceptionally skilled. Utterly schooled five armored guards with words and a wooden stick, simultaneously imparting a final lesson to Arya and a most heroic of heroic sacrifices, his words of wisdom continuing to resonate with her four books of horror later. Definitely the most epic death of the series.
"You shall be speaking to me with respect" indeed.
Living it's Barristan the Bold. The man taunted a friggin dragon. Fought as a mystery knight in a tourney at ten (losing or not,upon being unmasked everyone called him on his stones), casually slew the guards sent to capture him after he was cast out, then snuck back into the city to stare disapprovingly at the execution of Ned Stark, then went halfway across the world in time to save the Last Targaryen from a manticore wielding assassin. lost a "hard fought tourney" against the Kingslayer. At over sixty.
To reiterate there are a lot of parallels between Arya and Dany, to the point that I think they are being set up as foils to one another, perhaps even as reference to the "Song of Ice and Fire."
-They are both young noble girls on a "hero's quest" after being forced to flee to Essos following the deaths of their parents
-they both (erroneously) think themselves the last of their line
-they both empathize greatly with the weak, helpless, and lower classes, and seek to protect them and avenge them
-they are both passionate and have a strong sense of justice
-they both refer constantly to an older brother who played a major role in shaping their childhoods
-they both strongly identify with the sigils of their houses and have them as familiars
-they both suffer identity crises revolving around embracing their heritage
-they are both "magical" and very tied up in the "magical" component of the books' conflict
-they both have horse symbolism- Dany, the Dothraki, her Silver, her son being the Stallion that mounts the world; Arya- horseface, a good rider, wild and free spirited, her first kill is a stable boy i.e like a horse fleeing its captivity
-they both learn that their families weren't perfect (Arya learning about Wylla from Ned Dayne and how her grandfather came down on that town, Dany getting a few hints of her father's madness and realizing her brother was a prick)
-they both have a close bond with a burly knight with burly animal motif that betrays their trust and is a possible (and as of yet unrequited) love interest that is trying to reunite with them
-they both long for family and for home
-they both seek to return home to avenge the fall of their House and reclaim their birthright (well, at least under the FM
-they are both main (like top five) characters that have been on arcs utterly separate from other main characters and focused on their growth and quest for power/agency and purpose, and have stuck in Essos for the last two books
In addition to the parallels and possible foreshadowing, having Arya meet Dany would have a lot of potential both in universe and for character development. Dany has yet to truly confront the legacy of her father's madness- she has not encountered anyone linked with the Rebels. She strongly sympathizes with children and given their histories will most certainly be able to relate to Arya's arc. This will force her to confront the fact that the rebellion was not as cut and dry as she thought it was. Furthermore, Arya's ties to Jon and the Starks will prepare her to accept the R+L = J reveal and the necessity of going north to fight the Others. Arya will probably go to the Riverlands again to reunite with Nymeria et al (my money's 50-40-10 on Brienne, Arya, or the Blackfish offing Lady Stoneheart- and getting a flaming sword in the process) and will certainly make her way to the Wall as part of the final clash. But her leaving for the Wall right now does not have the same potential as her returning to Westeros with Dany.
I think she's going to be a handmaiden to a courtesan (learning politics and "girly stuff" poetry, song and dance, maybe glamors as well) then be with the Iron Bank for a third apprenticeship when Dany shows up to negotiate late TWOW.
Then she defects to the Dragon Queen and returns home with fire and blood, burning the Twins and meeting up with Stoneheart, Nymeria et al on her way north. After that, with the Others gone, the Wall and Kings Landing destroyed (I feel both will fall around the same time in TWOW or the next book) and the Seven Kingdoms splinter again? I could actually see her as a queen of the North, she's a born leader and all wildling by temperament, but I think, like the Stranger, she will be a wanderer, never really settling in any one place. Some sort of a Marco Polo Batman hybrid.
I am disinclined to believe either Harry-Sansa or Aegon-Arianne will come to pass.
Firstly, Sansa is already married to Tyrion, and unconsummated or not it will need the High Septon to annul it; and I subscribe to the theories that LF's plans will collapse around him. She will most likely throw in with Aegon, with a betrothal floated but (possibly) gone through with. She might end up married to him, she might not. I think she won't go through with it.
Each of the Starks will be backing a different claimant at least initially, and Sansa I think is going to be team Aegon.
Aegon, if he is real, is half Martell. He shouldn't need to marry into their family to get Dorne's support. Plus he will be wanting to marry Danaerys, and she won't be arriving for a while yet. He gains nothing and in fact loses quite a bit by marrying Arianne- a Sansa or even Margaery match would be better, politically, as bringing in a great house not tied to him already. There is also the possibility of the Reach going up in civil war- IIRC Tarly has an unwed daughter...
For all of Dayne's skill I think Robert takes it due to the fact that his weapon is far better suited at crushing through plate, and he's going to be pretty darn fast; look up some modern reenactments, a knight in armor is not at all like the lumbering giant depicted in fantasy cliches. The armor is what makes me favor Robert, more than anything else- swords, even magical two handed swords, are really really bad against armor compared to a warhammer, and Robert would also have better reach both as a person (he's likely taller) and with his weapon. That counts for a lot.
Also, on horseback I think a warhammer would actually be less useful than on foot,so Rhaegar probably had better chances mounted than in a melee, granted still rather poor given he's not on Robert or Dayne's level.
As a side note that lords trained at arms would be trained in the use of all sorts of weapons as well as hand to hand combat- even if Robert favored a warhammer and Dayne favored Dawn if they could both be reasonably expected to be at least competent with everything from polearms to crossbows.