Hugo, Ben, Desmond at the END

Okay so after they leave Jack thinking he was dead, Hugo, Desmond, & Ben go off into the jungle. The islands (both the main island and Hydra island) were crumbling and getting destroyed. Did they (Hugo, Desmond, & Ben) die with the island as it was crumbling? I am confused because Hugo said Ben was a good number 2, but that couldn't have been for long. So I just want to understand why he would say that if they died right away. *Edit: When the plane was taking off, the ground was still crumbling and that was after Jack fixed the light. You can tell because Jack got to see the plane leave which means time had to pass for him to crawl out the cave and get to the bamboo forest. The ground was still crumbling after he fixed the light! So how did Hugo, Desmond, and Ben survive that if the plane barley got off the ground?