If an RC Soldier is undergoing medical treatment and is approaching their REFRAD date, what options do they have for retention on AD?

If the case requires continued military care and possible civilian care for an issue developed on AD, then DEMOB station will determine the case and transfer said SM to WTU and their AD orders are extended for the duration of treatment.

AT demob they will determine if this treatment will require transfer to WTU.
If WTU is the course of action, you will be there until treatment is complete or further treatment will no longer result in improvement.
If the issue is not serious enough for WTU, the LOD that should have been completed will be used to bill followup treatment to Tricare in an MDAY or TPU status.

My understanding is they can be transfered to the WTU.