The subscription does not go to waste. If your inmate is released before the subscription period ends, the remaining issues simply follow them to their new address on the outside.
All you need to do is email aid@inmateaid.com with the updated address once he is home or has a confirmed address where he will be living. InmateAid will update the delivery address with the publisher and the remaining issues will be rerouted accordingly. He will not miss a single issue.
The same applies if he transfers to a different facility before release. If he moves within the system before the subscription ends, send InmateAid the new facility information and the magazines will be redirected there. Publishers are generally good about honoring address changes without interrupting delivery.
The only thing worth doing proactively is getting that new address to InmateAid promptly when the situation changes. Publishers work on a printing and mailing schedule, and updating the address before the next issue goes to print ensures a smooth redirect. If an issue goes out to the old address before the change is processed, InmateAid will work to get it sorted out, but the sooner the update happens the cleaner the transition.
So the four months you paid for after his expected release are not lost. They are just waiting for a new delivery address to be filled in.