Forcing file migration after deleting field
My current solution is to use a query, and manually cleanup the {migrate_map_files} table

$fids = db_query('
  SELECT mmf.sourceid1 FROM {migrate_map_files} mmf
  LEFT JOIN {file_managed} f ON f.fid = mmf.destid1
  WHERE f.fid IS NULL
')-&gt;fetchCol();

db_delete('migrate_map_files')
  -&gt;condition('sourceid1', $fids, 'IN')
  -&gt;execute();


reset the watermark in {migrate_status} and then re-run my files migrations.