Dear Rahul,
Your post contains a lot of confusing words, and the attachment is also not available. What do you mean by a compulsory retirement order? Is it a termination order? If so, okay.
Now, against the termination order, the employee appealed to the concerned authority, who upheld the decision. However, the Chairman and Managing Director rejected the order and ordered the reinstatement of the employee. After reinstatement, he was asked to submit his resignation again on 19-12-1998. Since the initial resignation was not accepted due to disciplinary action, he should submit a fresh resignation. This is necessary because there was a termination of employment followed by reinstatement. Therefore, as an employee after reinstatement, he needs to submit a resignation if he wishes to be relieved.
You mentioned that the "Letter of 19.12.98 cannot be treated as a resignation since he was not in service on this date and was seeking permission to resign as per officer service regulations." Why cannot the same be considered a resignation? You mentioned that the "filed review before CMD, which was allowed, and the officer was reinstated back into services." This indicates that he was reinstated into service.
The only issue is that his second letter of resignation was dated before the reinstatement. That resignation followed inducement by the bank's management, making it invalid. The officer can seek assistance from the CMD. This appears to be an old issue, possibly occurring around 24 years ago, and it seems you are still dealing with the technicalities of the matter.