I am writing this blog article under the conception that young Ben is now dead. However, if you watch LOST Untangled, frame 1:58 will drop a little nugget that makes me think maybe that isn't the case.
Anyway, onto my theory.... If young Ben is dead now, I don't think that means that adult Ben is. Because Ben already exists on the Island in 2007, I think that young Ben dying in '77 would not eliminate '07 Ben, but instead create a seperate timeline altogether. If Sayid going rogue has actually changed the future (which Faraday says is impossible), I believe that maybe, just maybe, the Oceanic 6's return was necessary to change the future.
Okay. Let me slow down here. With young Ben dead, the timeline will be vastly different than the one that adult Ben is taking part of in 2007. Two realities will be formed: one with Ben, and one without. It's my belief that the one without Ben could very well go on Purge-less, and that this reality's Island will proceed with DHARMA fully intact.
So that's my theory. If young Ben is dead, it doesn't mean that adult Ben will vanish from 2007. Rather, it just means that this particular timeline will forever be changed. Hopefully for the better.