That predictions were very delusional,not even HP hit $1 billion until the last movie and this movies are spin-offs.
FB1 grossed $812 WW so if FB2 gross $650-680 the drop wont be too big (HP1 grossed +900 while HP2 grossed +800,a drop pretty similar) but i think for the next movie JK needs help writing the script because the plot of this one is very messy and dense