First of all we need to understand what was the extent of the said plot.
Aerys II had placed wildfire caches on all key positions of the city which primarily included the city gates, Red Keep, Great Sept of Baelor and Dragonpit.
No one except chosen members of the Pyromancers, King Aerys & Jaime Lannister knew about it. Lord Chelsted came to suspect the plot and was burnt for trying to dissuade Aerys from using it.
Jaime later killed Aerys, Rosart, Garigus, Belis and other pyromancers involved in the plot but he never asked them about the locations of the said caches.
From ASOS:
“When I came on Rossart, he was dressed as a common man-at-arms,
hurrying to a postern gate. I slew him first. Then I slew
Aerys, before he could find someone else to carry his message to the
pyromancers. Days later, I hunted down the others and slew them as
well. Belis offered me gold, and Garigus wept for mercy. Well, a
sword’s more merciful than fire, but I don’t think Garigus much
appreciated the kindness I showed him.”
This means among the living people, except Jaime and Brienne no one has a clue about this last madness of King Aerys.
Later, Tyrion found out only the cache beneath the dragonpit. That means, the other caches are still soundly in place.
From ACOK:
“This cannot be true,” said Tyrion as he pored over the ledgers.
“Almost thirteen thousand jars? Do you take me for a fool? I’m not
about to pay the king’s gold for empty jars and pots of sewage sealed
with wax, I warn you.”
“No, no,” Hallyne squeaked, “the sums are accurate, I swear. We have
been, hmmm, most fortunate, my lord Hand. Another cache of Lord
Rossart’s was found, more than three hundred jars. Under the
Dragonpit! Some whores have been using the ruins to entertain their
patrons, and one of them fell through a patch of rotted floor into a
cellar. When he felt the jars, he mistook them for wine. He was so
drunk he broke the seal and drank some.”
But this quote uses the word another. Which means some of the caches were discovered previously, of which we do not know about. Nevertheless, it is safe to assume that most of the caches will be intact.
Other than that, there is also another intriguing thing. How much did Varys know? His little birds must have observed pyromancers coming and going. If that was enough to make a man like Lord Chelsted suspicious, surely Varys must have been so as well. Later, we know Varys knows many of the secrets of the red keep including secret passages. He might have discovered some of those caches beneath the palace himself.
