No. I would argue that not only was it not his undoing, it was how he came to win the Civil War and become the Dictator of the Republic. Initially at the outbreak of the war, Caesar announced he would respect neutrality and gave amnesty to those who surrender. such as to Ahenobarbus at the beginning of the war, who actually would come to fight him again. In contrast, Pompeians declared that all who were not with them were against the Republic. Caesar's policy of clemency may have convinced many to remain neutral and apathetic to conflict. What truly caused Caesar's death was his dismissal of his bodyguard because he did not believe his life was under threat and did not wish to give the appearance of fear. He is quoted as saying "I have lived long enough for nature or glory".

In conclusion, Caesar's clemency caused his death less than his lack of caution, and he gained great political benefits from his clemency, For more information on Julius Caesar, I recommend Adrian Goldsworthy's Caesar, Life of a Colossus.