Consider too, the scripture that says, "he will satisfy the desire of every living thing"
If 20 billion people are to be resurrected to a future Paradise Earth, how will they not desire to get married and have children? They wouldn't be human, but rather some peculiar reincarnation of their former self and missing their gender specific anatomy.
I believe we go to heaven when we die and we keep our personality and the thought expressions associated with our gender assigned at conception - the difference is we won't have the feelings to procreate - love, however, is another matter.