Recovering plants usually take quite a bit of time before they're restored to normal operation, and then quite a bit more time before they're actually thriving. One new root is a good sign--it will help sustain the plant--but the older leaves on the bottom, dying off, is the plants way of recovering the stored energy in those and transfering it to the new growth.
If it's putting out roots, definitely start a fertilizer regimen again. The plant needs to get its nutrients from somewhere, so by fertilizing, there's a very good chance it'll stop trying to get nutrients from the older parts of itself--I'll bet you'll notice it'll keep more of its older leaves as time goes on. Also, don't be discouraged--it can take several growing seasons for a plant to fully recover and start to thrive.