In your account settings there's a "Leave SimilarWorlds" option which displays this:
Leave Similar Worlds
This will put your Similar Worlds account on indefinite leave (Hiatus). After your account has been set to hiatus, once you complete the process, your account will be canceled and can no longer be reactivated.
If you choose to leave Similar Worlds, you will stop receiving email notifications, and also comments submitted on your profile and albums will be held pending approval by you.
You may reactivate your account later, by simply entering your email and password as usual at Log In, followed by pressing the Reactivate Account button.
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Frankly, it's confusing. It says it can't be reactivated and then says it can. I'd ask that question of the site management for clarification.