I'm pretty sure that all the forerunner are dead. It seems to me that in the closing days of the forerunner civilization, everything was falling apart, and that most options had failed. My best guess is if anything, forerunners survived on earth, because absolutely nothing happened to earth when halo went off, apart from the thawing of alot of glaciers and some unusual climate fluctutations.
That might explain why there are differen races on earth, if the forerunner were indeed human (we already know that primitive humans were living on earth at the time of Halo's detonation).
Or maybe they all died like 343 said they were.