you could probably make a system where you have 9 terrains loaded, you are in the middle one, and when you move and enter another terrain, switch the terrains so that the new one you are on is in the middle again, and load some new ones... (ie if you move to the terrain on the left, switch it right and reload the left 3 terrains).
That's what I said, fall_x. check the link!
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The idea is to have a 3x3 grid of identical terrains so that even though the view appears to be wrap-around, the camera will actually shift to the opposite end each time it reaches the boundaries of the central (original) terrain. So the player can traverse what appears to be a planet's surface infinitely in any direction.