If you sever the tap roots, you may wind up without the fine root hairs that actually do most of the work of transferring nutrients between plant tissues and the soil. There should be some near the base of the plant, but these are usually a small fraction of the fine roots.

You will need to balance the tops with the roots. Transplanting is essentially a root pruning operation. If the clump is big, you may be able to separate it with a few judicious cuts and get several plants out of it.

With nemerosa sages, this usually takes several years. Take advantage of this division to remove old, decaying tissue.

This advice is relevant to all basal rosette, alpine sages. A really thorough book on plants (including taxonomy) would include a description of the under ground components.