Impossible because of a few reasons.
The Maw is under the Jailer's jurisdiction. No prisoner has ever escaped. If Garrosh is in the Maw already than he should abandon all hope and just accept the fact that he'll be forever trapped there. Maybe his ambition might overcome the impossible but I highly doubt it. Keep in mind the only reason Sylvanas can actually go into the Maw and meet the Jailer then come back out is because she isn't a prisoner there. She's a employee or a business partner to the Jailer. That is the only reason she's allowed to freely come and go within the Maw.
But any prisoner no matter how powerful cannot escape the Maw ever. The official site states if these prisoners escape then all of reality will be destroyed. If these hardcore serial universe killers can't even hope to escape then there's no way a mere powerful orc like Garrosh or anyone weaker could. Now I understand Garrosh can ask Sylvanas to bail him out of jail instead of forcefully escaping but there's still the problem of would Sylvanas have any use for him. What could he do for Sylvanas at this stage?
Sylvanas will have no use for him and even if she did, would her business partner, the richer and more powerful of the two which is the Jailer even allow it? The Jailer is gonna need something big in return. But maybe just maybe it could still work if the Jailer somehow sees Garrosh having a high potential to become another agent for Garrosh himself might not be ok with it. The Jailer and Sylvanas is most likely planning to unmake the universe in their vision and Garrosh might not be okay with this unless they promise him the orcs will have a place to stay in the new universe. But now the question is would Sylvanas and the Jailer even be willing to let the orcs live once they recreate all of reality.
But there could be yet another option for Garrosh and that is to convince the player to release him. Nobody has ever escaped but if there was someone that could escape then it'll be the player's heroes. So Garrosh can pull a fast one with the player and then later he could betray the player and finish the job by murdering Anduin. But then what happens if he gets killed again. I'm sure the Arbiter will be very angry with him and would give him a bigger punishment once his soul goes to her again.