Unless there are plans to get rid of IDMS, why move the data out of IDMS.
You can remove the application code from the CV, keep the areas off-line or have a special DMCL that has just those areas and files. If you keep the schema, subschemas and reporting programs you can always run the reports in local mode.
If the plan is to extract the data into flat files, you will have all the same problems as if you were migrating the database to a relational database. You will need new programs to extract the data and generate reports.