It sounds like The Smurfs will be on their own for the third movie and won't be able to rely on humans. In an article at Variety on Sony Pictures, the trade says that the studio is fast-tracking The Smurfs 3 and that it will be entirely animated, compared to its predecessors which were live-action/animated hybrids.
The first film, which was released on July 29, 2011, cost about $110 million to make and earned $563.7 million worldwide. The $105 million second installment, released on July 31, 2013, took quite a dip in earnings, making $347.5 million worldwide.
The third film is scheduled for a August 14, 2015 release.