There are two types of devotees--the sadhaka, who is preparing for perfection, and the siddha, who is already perfect. As far as those who are already perfect are concerned, Bhagavad-gita says, tyaktva deham punar janma naiti mam eti so 'rjuna: "After giving up this material body, such a devotee comes to Me." After leaving the material body, the perfect devotee takes birth in the womb of a gopi on a planet where Krsna's pastimes are going on. This may be in this universe or another universe. This statement is found in the Ujjvala-nilamani, which is commented upon by Visvanatha Cakravarti Thakura. When a devotee becomes perfect, he is transferred to the universe where Krsna's pastimes are taking place. Krsna's eternal associates go wherever Krsna manifests His pastimes. As stated before, first the father and mother of Krsna appear, then the other associates. Quitting his material body, the perfect devotee also goes to associate with Krsna and His other associates. 

C.C. Madhya Lila 20.397)