If she dies, she'll be resurrected again, I'm pretty sure.
I think Genn or Tyrande are both possible though, depends on where Tyrande were when they burned down Teldrassil using a shard of Sargeras' weapon
The cinematic clearly showed that she finally cares about the horde, would be stupid to let such a powerful female character get washed away just because a few vocal people want her dead.