Yes, he will return now, this is not a spoiler, yet at least :)
Future storyline of wow 8.2 patch
Attention! Many spoilers ahead!
The storyline will most likely continue with the ask of Anduin to Jaina in order to save Bane. Jaina most likely will be ready to help since she remembers how Baine has risked his life to save Derek Proudmoore. Baine is supposed to be executed because he disobeyed to save Derek. In this mission Alliance will get help from Saurfang, Rohan and Thrall who will come back from his retreat. We all remember Thrall was not there since the start of the Legion content. Where Thrall has been ever since? Maybe lived with his family in the Alterac mountains. Probably Saurfang went to find Thrall and want him about what Sylvanas is doing with the horde and we all know she is not doing anything good, at least for now or at least we don't know the hidden agenda, but from what we can see, she is doing wrong and bad things.
On the side of horde there will be Lor'themar who will be saving Baine Bloodhoof. Sylvanas somehow finds out about Anduin´s plan and will wait for horde with ambush in the Vaults of Garrosh. Here many important things for horde occur, for instance new secret weapon being made from Azerite and further plans development so alliance could sneak into this base and see what´s horde has in the sleeve. After these events Sylvanas will sail into an open sea luring out alliance. All of them horde and alliance get into Azshara's trap as the result and appear in Nazjatar zone. There is a small possibility that alliance came into this trap because of Sylvana's will and that she was under the influence of some sort of dark deal ( maybe with N´zot!) Being in this trap Jaina explains to her allies that union with horde is necessary to be able to fight with Azshara, yet she notes that Horde will get satisfactory revenge for the Teldrassil. Also Jaina is sure that this union will help Thrall and Saurfang to get the riot ready. Thus truce will be somehow established, at least for now. Being in union does not mean that horde and alliance will stop blaming each other in different past actions lead to this moment.
Nazjatar and Azshara storyline
Azshara keeps huge masses of water with the Golganneth Stone so horde and alliance aim to get this stone and prevent Azshara to pull down all those masses of water to kill horde and alliance. We will be allowed to be in Nazjatar and even to kill Azshara´s subjects, in a place where Azshara controls every sand and shell piece, and every spell… there must be something wrong here. She aims to lure us all into her palace and to give a second born to all elves present here as nagas, to turn them. and then there will come new raid Azshara´s Eternal Palace. Meeting Azshara we will hear from her that heart of Azeroth will be used to open the N´zoth from his prison….
Who´s the next chief of Horde?
Have you noticed that Thrall appears in game when riot beings in horde? Also there are few questions will be left: who will be the next chief of horde and what will happen with Sylvanas? What were all her moves about and what they are supposed to lead her to? What role will Thrall play in patch 8.2 and further? We will play and take a look…