thinking about it, i think the fourth age might be pretty similar to the second age. consider the start of the second age. elros, from the line of luthien and beren, and tuor and idril, was the first to chose a mortal life, and in doing so, pretty much created the numenerian race. in the second age, they sorta grew cocky,probably because, in contrast to other men, they were superior, in just about every way. they also grew cocky thanks to the manipulations of sauron, but... sauron, as i recall, only enhanced the cockyness that was already there. in the end, they invaded valinor, demanding immortality, and in return, were pretty much killed off (and, of course, they had their island sink). valinor was, after all this, sorta removed from the plane in which middle earth lay in.
now, consider the fourth age. it starts off with the second elf in history chosing a mortal life. this elf being arwen. she, along with aragorn, already of numerian descent, will no doubt give rise to another mighty race of men. as with the numenereons, they will probably grow cocky, and then, in the end, they may try to even attack the elves that didn't leave for valinor, and the dwarves. the elves and dwarves will curse them, destroy minas tirith, but will, end the end, die themselves (this would be equiv. to the removal of valinor).