The short answer is that the employee does not have the right to resign
What if the employee changes his mind about resigning?
Source: Derek Jackson
I am quite often asked by employers what to do in instances where an employee has resigned, and then a week or more later he comes along and demands to withdraw his resignation. The short answer is that the employee does not have that right.
In SACTWU v Celrose Ltd  7 BLLR 944 (CCMA), an employee with 20 years service resigned after the employer had re-structured and moved to new premises. The employee “disagreed with the changes.” By the time the employee decided to withdraw his resignation, it was too late – the employer had already engaged a replacement. The employer did offer the driver a position as a casual employee, but he refused.
In his letter of resignation, the employee gave the reason for resigning as follows:” The reason for this is I am not happy working in the new Department. I disagree with the changes.”
There was a lot of argument in this matter – most of it contradictory. The position is that a contract of employment is a contract agreed to by two parties – the employer and the employer. Anything done under it must have the agreement of both parties. Thus, a resignation is tendered by one party (the employee) and the other party (the employer) agrees to accept it. In such circumstances, the termination of the contract has been agreed to by both parties. The employee therefore has no right to withdraw the resignation without the agreement of the other party – the employer. In other words, the employee has no legal right which entitles him to unilaterally withdraw his resignation.
The same principle applies to other issues revolving around the employment contract. Any changes (subject to certain conditions) to the terms and conditions of employment must be preceded by proper consultation and agreement between the parties to the contract. This would include changes to job title, functions and responsibilities, benefits such as medical aid, pension, car allowance, commissions, salaries and so on. It is equally important that any changes to the contract must be confirmed in writing. It is usually not necessary to issue a new contract altogether – it is only the changes that must be reduced to writing as an addendum to the contract.