Does deleting a field in a content type remove the data?
Deleting the field deletes the data too.
As far as I can see, the database tables used to contain the field data are renamed, but they are emptied. 

Visiting the page at admin/structure/types/manage/forum/fields, I deleted the "Forums" field used for the "Forum" content type; this is what I see watching the content of the database used for my Drupal test site, after I removed the field.



To notice also that the "deleted" column in the "{field_config_instance}" table is set to 1 for deleted fields.