Well, it is the management's prerogative to grant an extension of service to a retiring employee based on the needs of the organization and the value-added performance of the employee.
The employee could be given standard retirement benefits, settling his account and closing legal benefits like PF/superannuation, etc., to maintain accurate records.
Offer him a suitable retention appointment on agreeable and respectable terms for a certain period, with a salary package and benefits, excluding benefits like PF/superannuation, etc.
Practical aspects, such as whether this will set a wrong precedent tempting others to expect such extensions, or negotiate extensions, force extensions by keeping assignments pending, etc., need to be carefully considered and handled as a special case.
Moreover, sending a signal that high performers are valued by the company beyond the normal terms of employment and are taken extra care of, is a positive signal promoting employee retention and reducing the attrition rate, thus preventing employees from moving to competitors, etc., in my opinion. A straightforward case in isolation should not cause much concern, and other employees may also appreciate the signal as a step in the right direction by the management.
In fact, the trend, as we hear, is to hire retired employees as retainers with suitably designed packages even from outside for their valuable experience, which cannot be obtained from younger employees, especially when there is a talent crunch all around.
In a unionized environment, one may have to establish norms of objective practice to avoid a sense of favoritism towards certain employees, with a view to gaining the confidence of the union and preventing emotional objections and issues that may block claimed promotion chances of juniors in the pipeline - just mentioning this for awareness and consideration.
Granting a retention extension to a retiring employee is a good HR practice not to worry much about, in my opinion, based on the needs of the organization - in general.
One could consult with the labor advocate/consultant of the company for any implied legal issues and court precedents, if any, under certain circumstances - more for personal knowledge and to be on a confident footing.
Hope this helps.
Regards,
Kshantaram