They had no choice!!

[DharmaRecruit44]

The O6 had no choice but to "leave" the island, since it disappeared out from under them. You would think that if the island really wanted then that the helicopter would have came with it when it "moved"!

[Jaystar™]

The O6 had no choice but to "leave" the island, since it disappeared out from under them. You would think that if the island really wanted then that the helicopter would have came with it when it "moved"!

That could very well be or they could have been high enough to avoid from being dragged with it.

[islander]

The O6 had no choice but to "leave" the island, since it disappeared out from under them. You would think that if the island really wanted then that the helicopter would have came with it when it "moved"!

I think they were supposed to be on the freighter when it blew-up and take the "Jin Train" back to the island. We had a lot of debate as to why the heli didn't move with the island, but, LOL, what happens happened.

But you are correct that once the island moved to escape Widmore, the Losties, Frank and Des escaped the island and now the island is recalling them.

My theory is that the writers let the Losties escape so they could add a whole season detailing how they get back.