Destiny calling
Dave Filoni, when announcing that season 4 of Rebels would be its last, said this "We all felt that the time was right, and that the characters were at a point where their story, and their destinies, should finally be revealed."
So of course I can't help but keep speculating. Some fates are pretty much laid out, but I'll flesh out my thoughts further on the Force users of the Ghost. To summerize:
Hera survives, at least up to Endor. She remains a dedicated Rebel leader, likely with Chopper still at her side.
Sabine returns to Mandalore, likely involved in the civil war after the death of Gar Saxon and the reveal of the Darksaber. This could explain the absence of Mandalorians in the Original Trilogy.
Zeb remains with Hera in the Rebellion, or else returns to his homeworld Lira San.
Kanan and Ezra ... But let me sidetrack a little. Thinking about it, it seems that the show did actually foreshadow Kanan's blindness. In Relics of the Old Republic, Kanan was able to sense the AT-AT walkers through a sandstorm ie without using his eyes. That's the very same Force sense/sight that he'll need once he's blinded.
As for Kanan's and Ezra's fates ... well, this is what I put together. In the season 4 trailer, Kanan says "We are the Balance, Ezra. We were meant to be Jedi so we could be here now - when Lothal needs us most." I think this ties in with something Minister Tua said at the beginning of season 2, that she knew the true reason the Empire came to Lothal ... that there is another reason (other than the weapon/TIE fighter factories) known only to a few and ordered by the Emperor himself. And finally, in Rogue One, we see the Empire at Jedha, stripping the temple of kyber crystals for the Death Star. Put together, I suspect Kanan, with Ezra, destroy the kyber crystals in the Jedi temple on Lothal, denying the Empire and forcing it to turn to Jedha instead. In the process, Kanan sacrifices himself. I suspect that's the reason for the "We were meant to be Jedi" line, so they could access the Jedi temple, and in his sacrifice, Kanan dies a Jedi. Ezra, without a master, then drifts from the Jedi path. An unaligned Force user, likely believing in the Balance the Bendu talked about, and it's interesting to note that he's used both the Light and the Dark sides of the Force.
As for Thrawn, it's been stated that he isn't actually wholly loyal to the Empire. Thrawn's actually working within it to learn what threat it poses to his Chiss Ascendency. So I suspect the introduction of Rukh is to allow Thrawn to fake his death and return to the Ascendency, having learned what he needed. At least that wraps up Thrawn's arc without having to kill him, and leaves him available further down the line.