Could hit 2 billion, but not passing TITANIC. And the next two sequels(3 & 4) won't make at least that much, definitely lesser than 2 billion!
AVATAR 3 - 1.6bn
AVATAR 4 - 1.7bn
The only question is will FD become a TS3 or MU. If FD could become another TS3(better than or same as the first one) IM3 numbers is not impossible. But If FD becomes another MU( weaker than the first one or disappointing in quality) it'll fall short of Bilion, but still it'll reach 950m WW!