Oh well, since we are in metropolis, the plot is probably based on "Death of Superman" Storyline, if i would make a guess, Doomsday probably not "died" during their (him and Supes) final attack, or he probably killed Superman waay before the final attack and continued his rampage
Anyway, [url=http://dc.wikia.com/wiki/Doomsday_%28New_Earth%29]Here's the info[/url]