Fans have been suggesting that a Battle Back could bring Derek X. back into the game, but it's important to note that Battle Backs are usually for pre-jury evictees. Derek X. is in the jury. That's not to say that a jury Battle Back can't happen, but at this stage in the game, it's unlikely to happen, particularly due to the show having a shortened season.
That said, there are rumors that a triple eviction is coming in September. In order for a Battle Back to happen, we're going to have to see at least a double eviction, so the presence of a triple eviction looming means that we might see Derek X. back someday.
To see how it all plays out, catch Big Brother Sundays, Wednesdays, and Thursdays at 8 p.m. EST on CBS.