We have literally no idea. It has never been stated whether the escaped Forerunners survived the journey out of the milky way galaxy or not and the exact average Forerunner life span has never been determined. Because of this, we have no idea if they even lived long enough to complete the great journey, and considering the size of our galaxy and the amount of extragalactic space (the space between galaxies) between the milky way and whatever galaxy they were attempting to reach, those Forerunners might still be traveling that path to this day. So we have absolutely no idea about their status or whereabouts or what they have done since the activation of halo.