Rebels tells the canon story of how the Rebellion against the Empire developed until A New Hope. This leaves us with a bit of a problem though, three problems actually, Ezra, Kanan, and Ahsoka. It would seem that they would be present at the Battle of Yavin though I could see them skipping that, however by the time ESB rolls around Luke and Yoda are all that is left of the Jedi according Yoda. So what what happens to the heroes of Rebels? This is going to be pure speculation, there is nothing to back this up so far except the known canon.
There are two possibilities that can keep the stories canon. 1) They all die before A New Hope 2) One or more of them goes into hiding far away and Yoda thinks they are dead and since Luke hasn’t met them he does too.
Lets explore the least likely option, they are alive after ANH. In RotJ Yoda tells Luke that when he dies Luke will be the last of the Jedi. This implies greatly that all other Jedi are dead and we know based on S1:E8 Path of the Jedi that Yoda knows of both Ezra and Kanan. The logical conclusion is they died however this could be one of those Certain Point of View moments. Ahsoka is not a Jedi and neither is Kanan, they never completed their training. Also some time before ANH one or more of them could have left the rebellion, perhaps looking for allies beyond the outer rim or just escaping persecution thinking the rebellion would be better off without them. Vader and Tarkin seem to think they are dead by ANH and both knew of our three heroes existence. At the very least they have gone into hiding by this point and thought dead by the Empire and perhaps the Rebellion. So could we see them again? It’s possible, based on comments by Filoni back in April.
The most likely scenario is Ahsoka, Ezra and Kanan all dead before the Battle of Yavin. I know what you are thinking Disney won’t kill them its a kids show! The good news is they don’t have to, at least not on screen. I think it is likely that one of them will die onscreen, Ahsoka. She will most likely be killed by Vader, as a way to show us how callous and under the influence of the Darkside he is. She will sacrifice herself for the cause and drive home the sacrifice needed to be a Jedi to Ezra and Kanan. But lets say I am wrong and they won’t show the death of Ahsoka on screen, how could they all still be dead? As we saw previously they are already thought to be dead, most likely hiding out somewhere. That somewhere would be Alderaan. Vader spoke of Princess Leia’s mercy missions and it appeared that consulate ships are not attacked or boarded by the Empire. Its possible Leia or her father Bail rescued the crew of the Ghost who were thought destroyed. The message from Leia asking Obi-wan to go to Alderaan also leads me to believe she wanted him to meet up with the other known Jedi and the rebellion. Unfortunately he doesn’t make it there in time. The audience will know they are on Alderaan right before Tarkin and Vader show up.