What if the landlord doesn't refund the deposit if he loses his key?

Legal analysis: the landlord's handling method of not returning the deposit is to negotiate first. If negotiation fails, the landlord can sue for settlement. If the landlord's malicious breach of contract violates the provisions of the contract law, he can not only ask the court to return the deposit, but also ask him to pay liquidated damages in accordance with the contract.

Legal basis: Article 10 of the Measures for the Administration of Commercial Housing Lease, the lessee shall use the house reasonably according to the lease purpose and use requirements agreed in the contract, and shall not change the load-bearing structure of the house or dismantle or modify the indoor facilities without authorization, and shall not harm the legitimate rights and interests of other owners and users. If the lessee causes damage to the leased premises and facilities due to improper use, it shall be responsible for repair or be liable for compensation.

Article 11 The lessee shall obtain the written consent of the lessor when subletting the house. If the lessee sublets the house without the written consent of the lessor, the lessor may terminate the lease contract, take back the house and demand the lessee to compensate for the losses.