Yes, you can use the GPS legally, according to Jeppesen and the AIM, to fix VOR, NDB, intersections, or whatever else. In fact, using the GPS, the VOR or NDB doesn't even have to be working - the authorization specifically says the facility may be inoperative, and the GPS can still be used to fix it.
But if they take out the ADF, how will you be able to listen to Paul Harvey and Rush Limbaugh? Our pilots would cry and whine forever if the ADF were removed, and it's the first thing they'll write up in the book as inop.
I seldom if ever use the ADF, and LOM's are being decommissioned at a growing pace. Soon there will be few, if any, LOM's in existence in the U.S., and any excuse for use of ADF will be gone. My main complaint is that I still have to demonstrate testing the ADF during checkrides, even though it won't be used for anything during the ride, & the only thing it's used for on the line is listening to commercial broadcasts with the needle parked. I don't have the time or inclination for that, so I'd prefer it to be gone.