You have written, "He met the GM and requested him to take him back." What did the GM tell him? Will his services be continued or discontinued?
Recommendation on Handling the Situation
Secondly, no matter how strongly worded the letter you write, I recommend sending it under the signature of your GM. By bypassing you, when the worker approached the GM, you were left in a lurch. If you issue a letter and the worker refuses to accept it, you will be left in a lurch once again. Therefore, it is advisable to keep the GM in the loop and take appropriate action.
Discussing Punishment for Unauthorized Absence
Lastly, talk to the GM and find out if he is willing to impose any punishment on the worker for his unauthorized absence. This punishment is in addition to the forfeiture of wages for the absentee period.
Thanks,
Dinesh Divekar