It is not usual for the Almighty to suspend free choice to promote His ends. Biblical narratives are replete with examples of this principle. Many endeavors of the patriarchs, of Moshe Rabenu and of the prophets demonstrate it. Examples include when Abraham and Yishaq call their wives their sisters out of fear that they might be killed because of them, or when Yaaqob fears that Esau may annihilate him and all his family, notwithstanding each having received promises of future success absolutely incompatible with their death at those times. There is no guarantee to an individual that he will act appropriately and choose meritoriously to receive what is promised him if he does indeed succeed in being deserving.
Guarantees refer to potential.
Here, the prophet fears that going on a mission to fulfill a specific task given him by G-d may result in his death. G-d responds by providing him a pretext for his trip. Obviously, common sense caution is always required. Without it anything may happen. Let us turn to the case of Ribqah prodding Yaaqob to deceive his father to receive his blessing notwithstanding her foreknowledge that he was predestined to become ascendant.