What exactly is the issue? Is the problem from your side or from the candidate's side? You could have given little more information?
While raising a post on the public forum, and that too while seeking advice from the seniors, a member is expected to give complete information like when the offer letter was issued, for what designation, what was the date of joining, why the selected candidate sought an extension to join, why did he do that, how many times he backtracked from the commitment, what of correspondence you had with the candidate and so on.
Sans this information, how will it be possible to provide a draft of the letter?
Secondly, about the preparation of the draft itself. You could have prepared draft and uploaded it here. Some senior could have corrected it. Yes, there are few HR Managers who show overzealousness in providing the drafts even with inadequate information, but then this kind of spoon-feeding does a great disservice not just to the individual who seeks the draft but to the HR community as a whole.
27th May 2019 From India, Bangalore
In future in the offer letter itself always please include point as below
"This offer is valid till ____ only and your failure to report to duty on or before ___will lead to cancellation of this offer without any further communication."
For current case you may write a email as below
"With further reference to our offer letter dated ____ issued to you,please note that our offer letter stands cancelled with immediate effect, as you have failed to report to office on____ as committed by you.
27th May 2019 From India, Madras
Did the candidate inform you his inability to join your company? If, has informed there is no need to send a revocation letter for Offer.
Always insert a line in offer letter so that you would not have to send revocation letter;
"This offer is valid till date.--------------which stands cancelled as you failed to join by the date, without making any further communication to you."
27th May 2019 From India, Mumbai