But the 3d content can be recovered if necessary. Simply select the revised marker:
Right click and select Restore All Interior Elevations in Group:
The original (non-deleted) elevations and their 2d content will remain unchanged. The restored portions of the elevation marker will now be available and restored to the original condition. Again, just to emphasize, the 2d drafted content of the deleted markers can NOT be recovered. But there is no need to delete the entire marker and start over.