Retention of Govt. Quarter

An employee is to vacate the Qtr. on the date of retirement/ death /transfer.
Specific order from Head of the department is required for any extension and in that case the employee is to pay the local market rent or at such amount ordered by the Head of the Department.

Thanks to both of you.
If competent authority grants the extension for a time period of six months; then how the rent will be paid?
Also please mention the process of finding out the local market rent.