Legend is the first installment of a trilogy, What do think is in the store for Day and June in the next book series?

 That of course is up to speculation. My guess would be as good as yours. At the end of Legend, June and Day decide to go to Las Vegas, a Colonies stronghold, to check on Tess, who has joined the Patriots. After that, they will go to the warfront to rescue Eden. What happens from there depends on your imagination unless you checkout the next book.