As the judgment is not to be before the end of the world, how do you say that some men will then be alive, and thus will be dead, seeing it is appointed to all men once to die (Heb. 9:27, 28)?

See Heb 9:27-28 - Paul answers this question when he says, that those who then survive will suddenly be changed so that their corruption will be abolished, and their bodies will put on incorruption (1Co 15:52; 1Th 4:17).