The way I see it, maybe the goddesses will get alternative bodies, like Vulcan in Tsukiyo's doll. Thus they can 'stay and interact' with their hosts and Keima, trying to raise their flags in the love ranking
The story still has some points it can cover, like what happens to Vintage after the Weiss are sealed again, what happened to heaven (the place Diana&co come from) and why they didn't try to help with the hunt for souls.