Funny one would think that if they wanted to be plain that Thrall was coming back, they might not simply say we are getting our Warchief back. They might want to say something like Thrall is coming back or follow up that little line by making it clear that when they say we are getting our Warchief back they mean Thrall. The fact that someone said we are getting out Warchief back and then explicitly left Thrall's name out of it is a far far stronger indicated that Thrall is not coming back then that he is.
The fact that you got that Thunder is coming to mean that Thrall is coming back as Warchief is at best a stretch.
I understand you are very very very passionate about Thrall coming back, but I don't really see any actual evidence to support it.
Then again maybe I am not "true Horde" and thus did not get the clarity of the message.