Yes and maybe this is what happened again -- that once he left, he couldn't find it to get them? So this would mean that they don't all get rescued. Although we see Claire getting on the copter....hmmmm

I had forgotten he told Kate he'd return for her. Okay so he's still on the same track.

I thought Kate`s reaction seemed kinda weird in the FF, like she wasn`t at all interested in going back. And she is always the one who wants to go back for everyone. So maybe it isn`t that they left someone there, but Jack finding himself unable to get on with his life and realizing he should have stayed at the island?

Do you think Jack would not be so insistent on the island to LEAVE, had he been made aware of its healing properties?

Like knowing about Rose's cancer being cured, and Locke walking?