Lease Extension with fewer tenants

[Artem Kovalevskiy]

Been a while since I've posted on here! Keeping busy with renovations on my second property! 

I finished my 1st house about 6 months ago, and it has been rented out since June. I decided to do a probationary lease (2 part) for 7 months, and if there were no issues in that period, specifically with late rent (which so far its been paid on time), I would extend the lease for 5 more month, and after that if my tenants choose to stay, we would then do the traditional 1 year lease. So this brings me to my question. One of the family members is having personal health issues due to age, and will not be "renewing" the lease for the 5 month period. What do I do with the current security deposit, I know that they will want their "contribution" back. Do I just keep the whole deposit, since its a lease extension, and let the other roommates reimburse the one that leaving? Thank you in advance for the advice and guidance!