This is just my opinion you understand, but I would divide the plant. When repotting a large one, particularly with growth/roots that were never maintained, dividing will allow you to manage the size of the pots/baskets and allow your plants room to get some air, which should benefit the viable roots you have. This will also allow you to more easily separate the roots and undo the matting. There is probably no medium left below this mat of roots because it has all disintegrated over time. The viable roots were simply using the dead roots as its growing medium! I agree you should keep the plant(s) in a shaded area (perhaps one with a couple of hours of early morning sunlight), one where you can control the moisture, and where the plant(s) will get good air movement. Good luck. Ken
