There’s a couple points I’d like to make about this.
First off, questions about Tally Hall merchandise (past, present, and future) can most likely only be answered by the band or someone involved in the Tally Hall camp. You can contact them through their website at www.tallyhall.com.
That said, I can tell you that Tally Hall makes great efforts to always stay fresh and new with everything they do. If they feel that design has run its course, then I guarantee another new and clever design will be replacing it. Their latest batch of shirts seemed to dwindle short as their tour was running down so perhaps they tried to order accordingly and ran out of some things earlier than others. It’s possible they may bring it back but I believe they have also been working on new designs, too.
If you want a design back, flood the band with requests for it! (One per person, please. They get a ton of email already.)