I have a pretty solid theory about something that they might show in the future... When Juliet blew up the bomb into Season 6, she experienced the same exact type of flash that Desmond experienced in "Flashes Before Your Eyes". Her mind flashed back to sometime in her life and she couldn't exactly figure out what was going on. During her flash, however, Eloise visited her. She assured Juliet that their plan had worked, and told her to tell the rest of the Losties that it worked. Juliet was then talking to a guy (possible Sawyer, we don't know) when she flashed back to the present. Confused, she started talking to Sawyer as if she was talking to said guy, and then realized what was going on. However, she died from her injuries before she could tell them that it worked.
This would also infer that whatever happened to Desmond with the failsafe was similar to whatever happened to Juliet in blowing up the bomb. Perhaps, a massive amount of exposure to electromagnetic energy? Also, this theory explains how Juliet woke up so much higher up in the hatch hole than she had fallen in. Remember how Desmond woke up on the ground?