According to the clue Monk Emperor had given through the Heart-Illuminating Mirror, obtaining the Blood Pill meant they could dissolve the Blood God Pill within Nameless's body. Once Nameless fully regained his strength, Jiang Dali believed dealing with Di Shitian would become much easier.
And even if they could not kill that old monster, whose Qi and Blood was abundant and who was exceedingly troublesome, they should at least be able to wound him severely again, preventing him from stirring up trouble in the martial world and making it difficult for him to threaten Jiang Dali again anytime soon.
In Jiang Dali's book, any enemy unable to threaten him for a short time would usually be completely unable to threaten him after that period had passed.
At the end of the day, the reason he was so determined to deal with Di Shitian was that Di Shitian's various dark and harmful methods had gradually begun to threaten his safety. Even Immortal God had fallen for his schemes at the height of his power, and even Qin Shi Huang of Qin had been tricked by that old schemer. Jiang Dali did not believe he could guard against all of that old schemer's underhanded tricks.
Moreover, Di Shitian's ambitions would inevitably lead Heavenly Gate into a serious conflict with Black Wind Stronghold. With both survival and interests clashing, it would be difficult to bypass that tough old monster. Otherwise, Jiang Dali could simply have let the matter go and ignored him.
After all, while there were not many old monsters like this lurking behind the scenes of the martial world and stirring up the winds and clouds, neither were they particularly rare among the Vassal States. The Great Mountain Lord of Xuanhua Hao in Ying was also mysterious and immensely powerful, but