Grommash resurrects Garrosh with his final breath and the power of friendship.
Garrosh takes Gorehowl back and escapes back to our Azeroth.
He sails to Northrend and scales Icecrown, then uses a new mineral he happened to discover along the way called 'Metzenite' to fuse his body with Bolvar's.
Becomes Bolvarrosh Helldragon, the Iron Lich, raising Orc corpses to purge the Scourge of non-Orcish undead.
Undead-undead Drakkari as the obligatory troll raid.
Something about Thrall.