If there is very little light getting to the lowerparts of the plant, it will rot. But the tops will continue to grow, sending roots into the substrate to hold its self down.
It loves bright lights, mine mostly take in ferts from the water column.
To keep it looking good all the time, you have to either trim off the bottoms and replant the tips every once in a while, or give it good trims each week - depending on how fast it grows