Security Deposited Refund or Not

[Hai Le]

Garage tenant entered 6 month lease for May into November $850 a month. Lease agreement states security deposit would be used as an unpaid rent if there was early termination.
Tenant decides to end lease early making final payment August 1st and moving out the 3rd, I find a tenant September 1st but at a rent payment of $700 instead of $850  
Does this tenant have the ability to get his security deposit refunded if it took a month to find a new tenant after he had left? 

[Lien Vuong]

If they paid you for August and left during that month then you dont have any back rent. What you can argue is using the SD to make up the differential since you are low losing $150 monthly because of their early termination. Sept to November would be 3 months x 150 would be $450 - $850 so balance returned to them would be $400.00