Begs the question: were people so impressed and surprised? We get that sense from the OT because the point of view is from within the small band of the main characters. Also, even at their height, most people never saw a Jedi. But I doubt the leadership of the Rebellion was so unaware, most of them would have lived through the Clone Wars. I think Rebels is showing that there was a lot more interactivity and awareness than we expected, and there's really nothing in the OT that precludes it.
You would expect, however, with people like Hera, Kanan and Ahsoka around they might have played a larger role in the whole assault on the Death Star, or the second death star. Rather than Lando in the Falcon, Hera leading the charge would totally make sense there.
That's a pretty big leap. Rebels takes place some 5 years before the Battle of Yavin, and the Battle of Endor takes place 4 years after that again. Lots of things could have happened to the crew of the Ghost in those five and nine years to account for why they weren't there.
Begs the second question: why did anything have to happen to them? I think you guys are suffering from "Small Galaxy Syndrome"
One of the things I think Rebels is *intentionally* doing (and will continue to do) is expand the universe beyond what we knew in the OT. I don't just mean the cast of characters, but the entire scope of the Imperial reach and the Rebel effort. Sure, maybe the OT story was the key story -- because of the whole "Chosen One Brings Balance" theme and the eventual death of the Emperor -- but it was only one of many. The galaxy is huge, and there would have to have been multiple, simultaneous, and even unrelated Rebel efforts going on all the time. Hera and crew could have been doing something extremely important on the other side of the galaxy. Or maybe, given Kanan's reservations about the military nature of the Rebels, after Alderaan they might have decided to lay low and stick to doing good in a smaller way..."think galacticly, act locally" if you will.
tl;dr - not every story has to be tied to the OT, and there's nothing unreasonable about the Ghost crew not being involved in the OT scenes.
As for Ahsoka, I agree she's probably doomed. And her last words will be: "There's still good in him."