Faustus has reconsidered his deal with the devil, and considers repentance. However, he never goes through with it. It becomes quite obvious that he would simply rather live his life of damnation, than give it up for the life of a mere mortal who’s soul would be saved. It is established earlier in Act V that, if Dr. Faustus were sincere in wishing to be with God, Mephistopheles and Lucifer would have no power to prevent him from doing so: Mephistopheles says of the old man, "His faith is great, I cannot touch his soul," and we have already learned in Act II that Lucifer would have not even the power to torment Dr. Faustus' body, when the Good Angel says to Dr. Faustus, "Repent, and [devils] shall never raze thy skin."
He also exhibits very supercilious and pretentious behavior when he tells Mephistophilis, “This word ‘damnation’ terrifies me not,” and he even goes so far as to say “What, is great Mephistophilis so passionate For being deprived of the joys of heaven? Learn thou of Faustus manly fortitude And scorn those joys thou never shalt