I agree with eskura. In season 1, I've seen many a battle where there was a doom card and Dan-or any other brawlers'-bakugan were sent to the doom dimension but not the opponent's.
I'm guessing that you lose your life gauge by the g-power of your bakugan. eg. Pyrus Helios@ 450 gs after abilities and gate lost- 450 gs or points of your life gauge would dissapear. This goes on until one player has run out of points P.S. One bakugan can be used multiple times.