Garrosh will die.
They had the rough story line plotted out when they made him warchief in Cata.
When Garrosh was made warchief, his mission in the overall plot was to bring darkness
and dishonor back to the Horde. He is doing the same thing Grom did to the Horde,
but without the demon blood. Thrall could never do things so dark to reignite the
Horde vs Alliance war. So they put Garrosh as warchief to be nasty for a while
then we kill him. Garrosh has to die for the WoW storyline to move forward toward
the next expansion.