Boracare takes care of any active infestation of wood-destroying insects such as termites, carpenter ants, powderpost beetles, etc. It is possible for the wood to become infested again if it has been exposed to water, if the wood wasn't treated in any way, like if it wasn't stained, after the Boracare treatment dried or if not all exposed sides were treated.
Although, from the information you provided regarding the termite tunnels, if you're talking about mud tunnels then you are dealing with Subterranean termites. Boracare will still affect them if the eat the wood but the method of treatment to get rid of the colony will be to do a trench treatment around the Perimeter of your home with Termidor. Termidor can't be used indoors unless it's sprayed/foamed inside an enclosed wall void.
If you are sure, however, that you are dealing with Drywood termites, we recommend that you call Nisus (800) 264-0870 to troubleshoot with them as they are the makers of Boracare.
Boracare is specifically designed to be applied to plywood and any other raw wood surface that hasn't been stained or finished with anything like paint or a sealant.