Good theory, although I think we are just seeing their lives without the island having been involved as it had been before (Flight 815 crash).
So, what appears to be a "different/redeemed" life for all of them is actually just a spot on an alternate timeline that will ultimately bring them all back together again. I think that Miles being Sawyer's partner is evidence of the course correction that is occuring, and which will always occur. Whereas the rest of the Losties having run into each other on the plane is the same as it was in the original timeline, and makes a certain amount of sense, having Miles and Charlotte thrown directly into Sawyer's "alternate" life suggests to me that we're just watching events before another big course correction occurs. And, notice, although roles have appeared to change a little, the people themselves are still the same in one way or another. When you break it down, a Sawyer with a "sentimental" heart as a cop is still no different than a Sawyer with a "sentimental" heart who is a con man. He's still the same person inside regardless of the day-to-day choices he makes, and regardless of what his profession is. The person in both roles still has the same values and will ultimately arrive at the same conclusions in life, no matter what (or how different) their choices are in the lives they lead.
It's the same as Desmond having been given an alternate reality a few seasons ago, where he chose to go and buy the ring instead of enlisting in the military. Eloise was the one to point out the course correction. So it doesn't matter what any of the Losties do in the alternate reality. They'll still all end up on the island again.
