My only concern would be, if you get rerouted LHR/ATL/BOS, your bags will be tagged to BOS. If you arrive ATL at Concourse F - NO PROBLEM - you just leave the airport with your bags. If you arrive ATL at Concourse E, you can't take bags thru TSA security (which you'll need to dao to get out of the airport) if they have any liquids, sharp items, etc, in them.
Is there a chance you won't be checking any luggage on the way back?