I know it was not really explained but why do you think Ben told Jack that they ALL would have to go back?

Good thought, indeed, it does seem that only Jack wants to go back, so if they did eventually return, would the rest of O6 just sit in a huff on the beach?

This brings me to the conclusion that they were meant to be on the island, even it i for a seemingly unknown purpose.

I don't know what he means by all. I'd like to know if he just means the O6 and Locke, or everyone else like Frank and Desmond as well.

and walt. it looks like the timelines caught up with him now so maybe he'll be in more episodes