For one who very seriously practices devotional service during his lifetime in order to understand the constitutional position of the Supreme Personality of Godhead, liberation from this material world is guaranteed, even if he has previously been addicted to sinful habits. This is also confirmed in Bhagavad-gita:

Even if one commits the most abominable actions, if he is engaged in devotional service he is to be considered saintly because he is properly situated. (Bg. 9.30) The only purpose of life is to be fully absorbed in thoughts of Krsna and His form, pastimes, activities and qualities. If one is able to think of Krsna in this way, twenty-four hours a day, he is already liberated (svarupena vyavasthitih). Whereas materialists are absorbed in material thoughts and activities, devotees, on the contrary, are always absorbed in thoughts of Krsna and Krsnas activities. Therefore they are already on the platform of liberation. One has to think of Krsna with full absorption at the time of death. Then he will certainly return home, back to Godhead, without a doubt.