Recover a deleted field
A good question, and surprising there's not an easier way to rollback a deleted field, given the data is still available.

Assuming you have:


Renamed the field_deleted_* tables back to field_data_field_myfield and field_revision_field_myfield (latter also important)
Updated the 'deleted' flag from 1 to 0 in the relevant data tables.


There is also 


field_config



  The main field configuration



field_config_instance



  The field configuration on a particular entity bundle.


You may need to adjust the 'deleted' flag there also:

e.g:

UPDATE field_config SET deleted = 0 where field_name = 'field_my_deleted_field';
UPDATE field_config_instance SET deleted = 0 where field_name = 'field_my_deleted_field';
TRUNCATE TABLE cache_field;