Questions about humans who are waiting, in some sense alive, until the Battle of Battles are unlikely to have definitive answers. Christopher Tolkien did not include Mandos' prophecy regarding the Dagor Dagorath in the published Silmarillion, because his father's thoughts about the battle had changed significantly over the years. One of the major issues with the prophecy was the role of Turin, who, in early versions of the legendarium, had become immortal and would be Morgoth's final slayer. Yet this was not consistent with Tolkien's eventual view of the Gift of Men. There would be similar issues with the surviving invaders from Numenor.
Of course, we know from The Lord of the Rings that it is within the power of the Ainur to keep men "alive" beyond the natural span of their years, as Sauron did with the ringwraiths. However, their total "life" had to be stretched out over a longer and longer period, robbing them of their human characters. If the armies of Numenor were kept alive in the cave, they might similarly have become worn out remnants of their former selves; or they might have been held in suspended animation, waiting to awaken for the end of days.