Anubias are extremely hardy. I wouldn't worry too much about damaging the roots when you separate it from the driftwood. I have split Anubias many times, and for me at least, part of the process means pruning the roots, especially in a long established plant. I have had roots that have been about 6 inches long. I cut them down to about 1 -1.5 inches and replant. When you plant them, make sure the rhizome isn't buried because that will kill the plant.