Regarding Han Dong's invitation,
The Terror Source High Priest and Chief Engineer Heize decisively refused.
"Covert assistance" and "going to one's death" are two different concepts.
At present, the two's transgressions and escape had no direct connection with Han Dong... Even without considering the danger of the Underground area itself.
Should Han Dong's 'power-snatching plan' fail and the Pharaoh and his Personal Guards pursued the matter, the two would have a slim chance of escaping death.
Having held his position for so many years, the High Priest was very clear about how stable the current Pharaoh's position was.
Moreover, the Pharaoh himself was very powerful... and as a "Node holder," the Pharaoh was bound to the City of Gods.
If needed, he could even harness the power of the City of Gods for his own use.
The High Priest did not wish to "go to his death"; he only wished to assist Han Dong without compromising his own interests.