Delete/cancel a Drupal user programmatically and safely.

gistfile1.php

  // Tell Drupal to cancel this user.
  // The third argument can be one of the following:
  //   - user_cancel_block: disable user, leave content
  //   - user_cancel_block_unpublish: disable user, unpublish content
  //   - user_cancel_reassign: delete user, reassign content to uid=0
  //   - user_cancel_delete: delete user, delete content
  user_cancel(array(), $uid, 'user_cancel_reassign');

  // user_cancel() initiates a batch process. Run it manually.
  $batch =& batch_get();
  $batch['progressive'] = FALSE;
  batch_process();