Once a soldier is referred to the IDES, the MEB phase of the process will begin. The MEB phase of the IDES process will take place at a Military Treatment Facility (MTF) located in CONUS where a comprehensive evaluation will be conducted by a Department of Veterns Affairs (VA) doctor. Once the VA evaluation is returned the the MEB, it will review the evaluation and determine if any of the soldier's conditions fail retention standards. A narrative summary (NARSUM) and a DA Form 3947 will be issued once the review is complete. A soldier is then given 7 duty days to respond to the NARSUM and the results of the review. If the MEB findings determine one of the soldiers conditions do not meet retention standards, the soldier will be referred to the Physical Evaluation Board (PEB).
Due to the use of VA doctors, soldiers assigned OCONUS will be required to PCS to a WTU at one of six designated CONUS locations for completion of the IDES. Currently, the Army's are Ft Bliss, Ft Hood, Ft Sam Houston, Ft Gordon, Ft Bragg, and Ft Lewis. Similarly, other branches have predetermined locations. Ideally the soldier would PCS to the WTU closest to home/family, but that's not guaranteed.
As with everything, there are always exceptions to policy that may provide relief from the requirement to PCS back to a CONUS location. Some exceptions would be Dual Military assigned in Europe where it's impractical to PCS spouse, soldiers who are European citizens and desire to stay in Europe after military service, or if there's a significant illness or disability of European family members. With the newness of these IDES changes, the outcome of applying for an exception is unpredictable. Regardless of which branch of service you are in, this is backbone of the process up to what you're asking about. There's always going to be local and branch specific policies and procedures, but it should always ( in a sometimes roundabout way) coincide with IDES guidelines. I hope this helps.