Like Facebook, your profile would be inactive but if you ever choose to come back you can!!! Because sometimes you just want to take a break but you don't want to lose all your XPER if you come back! But we also keep the permanent option as-well!
If you're really desperate for some self-control, change your password to something random that you won't be able to remember so that you won't be tempted to log in. When you're done with your break you can always change it again later.
There's not really any technical reason why it couldn't happen. I can't really think of any "operational" reason, either. I can understand the reasoning behind not being able to change your username. As in my case, however, there are two sets of questions and opinions by the same person, with different usernames because I deactivated, regretted doing so, and came back. It would have been much better for me to still be that original user.