In the last episode of Star Wars Rebels "Family Reunion - and Farewell: Part II" we see that:
Ezra fights his way to Thrawn, and reveals that he arranged Mart to call the purrgil, who arrives and destroys Thrawn's fleet. The purrgil then grab Thrawn's flagship and ready to drag it to hyperspace. Despite pleas from his friends, they have to be convinced that they are defeated for good, and they jump away.
When
catch
Thrawn,
they
break all the windows of the ship. All windows of the control station where Ezra and Thrawn are located are broken...
Then they
flee into space in light speed.
As a result, when the ship enters space (and hyper space), how could the people on board survive?
(Will Ezra act in the same way as Leia did in TLJ ? :) What about Thrawn ?)
I’ll say this much: they’re not dead. Both of them survive, both Ezra and Thrawn I would say survive it.
The answer is therefore it is unknown and you'll have to wait for the new series.