Although prophecies do not guarantee absolute certainty, they at least indicate a significant chance of success, which coincides with the Skambuhe National Master's prophecy that their chances lie in the north, not the south.
However, compared to Skambuhe National Master's vague prophecy, Sazass's prophecy is perhaps too detailed.
Either this chief of the Necromancer System also specializes in the Prophecy field, possessing extraordinary prowess in this area.
Or he used the prophecy to speak his own mind, mixing much personal content in truth and fiction.
Either way, Khan Yamun does not care, because the plan is just a plan; how to execute it is his matter.
If a better opportunity arises, he certainly wouldn't delay one bit because of a so-called prophecy.
Just as he didn't easily spare the Kingdom of Ser because of the Skambuhe National Master's prophecy, any probing must be conducted.