If you are using the stb only for OTA that means you only need to have the antenna connected. You don't need to have the Voom dish connected any longer. Why not just disconnect the dish cable (where any signal would be sent) and continue with the antenna cable? That's what I did until I got DISH.
I posted this many times before: There is no timebomb in the STB! (For OTA, anyway). This is coming from VOOM engineers who are supposed to know this stuff.
The rumor about STBs going dark in June comes from CSRs who are told that all accounts are in the process of deactivation. Yes, in the past account deactivation would trigger the kill signal (sent via satellite). Today, the satellite is dead for all practical purposes, so the kill signal cannot be sent (and there is really no need to). If you still have some worries, disconnect from the dish if you haven't done that yet.