Praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
In principle, Ijarah contract is binding and may not be terminated by the will of one party, so if both parties have agreed on terminating contract before it expires then this is permissible and the lessee is liable for paying the rent due for the whole period in which he had benefitted from the property. An-Nawawi {May Allah have mercy on him} said: "Once the lessee takes possession of the property, he becomes liable for paying its rent for the whole period of contract." {Menhaj At-Talibeen, Page: 163}.
Upon termination of contract, if the specified rent is divided over months, for example, the lessor and lessee agreed on leasing a car for three years; a certain sum for each month, then the lessee is liable for this specific sum without taking rent of similar properties into consideration. It is stated in {Hawashi Ash-Sharwani Ala Tohfat Al-Mohtaj Fi Shareh Al-Minhaj, Vol.6: P.187}: "If he divided the rent over months, then the lessee is liable for paying this specific sum without taking rent of similar properties into consideration."
In conclusion, it isn`t permissible for the lessee to terminate the Ijarah contract except with the approval of the lessor. If the latter approved of this, then he is entitled to receive the specified rent for the period in which the lessee had benefitted from the property, as agreed upon conclusion of contract, and he (Lessor) doesn`t have the right to demand the rent of similar property because the contract was terminated by mutual consent. However, he (Lessor) can obligate the lessee to complete the whole period of the contract. And Allah the Almighty knows best.