First a couple of ifs/assumptions: 1) there can't be anything else in the lease that would continue to make it valid other than producing gas, such as gas storage or an oil well (in fact, the well might actually be an oil well), and 2) the well really can't be producing, which you can confirm if you get a gas expert to do an "open flow" test that will tell what, if anything, the well is producing (although you better be about absolutely sure b/c it's a misdemeanor offense in PA to blow someone else's gas into the air). If these 2 ifs/assumptions are true, then it doesn't matter a darn bit if the lease covers from the surface to the center of the Earth b/c the lease is ended/breached.
Before you call the DEP, get the GPS coordinates, Lat. and Long. if you can, this will be helpful to the DEP to look in their records. Sometimes well will have a tag on them with some information on it,