It really wasn't his fault. No matter what his nephew said, Iroh knew that the young man's life was not over. He was merely exaggerating.
It was something he was prone to, really, the old man mused. Zuko was always ready to go off half-cocked and do something stupid and then moan about it like the world was coming to an end.
Case in point: Iroh had merely suggested that a nice set of tea would be an acceptable present for the Lady Mai's birthday. Everyone likes tea! Apparently not the Lady Mai. Iroh shook his head. From what he'd heard, Mai had tossed the wooden box at Zuko, and it had come open, spilling leaves all over him. Then she had dumped him.
Which is what caused the most recent bout of his nephew's exaggeration. His life was most certainly not over and the world had most definitely not come to an end.
However, that didn't stop Iroh from sending a black ribbon messenger hawk to the Southern Water Tribe to warn Master Katara that the world was ending, Zuko's life was over and her presence was required to fix the problem.
She was there in under a week.