By the end of the novel, both Victor Frankenstein and his creature have been destroyed by their desire for revenge. Victor has sought to avenge the deaths of all his loved ones -- William, Justine, Henry, Elizabeth, and Clerval -- and it has completely and utterly wasted him, physically. On his deathbed, he asks Captain Walton to swear that he will not let the monster live, "'that [Walton] will [...] satisfy [Victor's] vengeance in [the monster's] death.'" He begs Walton not to listen to the creature but to "'call on the manes of William, Justine, Clerval, Elizabeth, [Victor's] father, and the wretched Victor, and thrust [his] sword into [the monster's] heart.'" Victor declares that he will "'hover near" and help to aim Walton's sword. His desire for revenge surpasses even his desire to remain alive; Victor has given up on his own life and only cares about his revenge now: such is the destructive power of revenge.
Confronted by Captain Walton over the dead body of his creator, the creature says, "'[...] I was the slave, not the master of an impulse, which I detested, yet could not disobey [....]. Evil thenceforth became my good.'" His desire for revenge changed him, made him a thrall so that he seems to have no agency of his own; he could only seek to satisfy his need for vengeance. It has consumed him, and now there is no reason left for him to live. He vows to end his life. His need for revenge has destroyed him.