Participating sites should have a checkbox when submitting:

[ ] Check here if you wish for your theme to remain only on this site, otherwise, it may be included in the Litestep repository.

If not, a clear "Terms of Agreement" should be displayed when uploading a theme.

As someone who is still active in the Litestep community, if my theme were to be relocated, or modified, without my permission, I'd be pissed off.

If I was inactive for a long period of time, I'd expect an attempt to be made to contact me before modifying, or moving, my theme. Failing a genuine attempt at contacting me, I'd be understanding of whatever may be done with my theme, as I personally would then consider it to be abandoned. Others may not feel that way. Keep in mind, copyright laws do not recognize something as being abandoned for up to - if I remember correctly - 70 to 120 years, depending on conditions.

edit - For the record, I'd never expect someone to actually sue over a Litestep theme. What damages could you really expect to be compensated for.