Inform the tenant that agreement is for period of one year 

on expiry of one year he can vacate the premises 

there is no question of refund 

Even if the oral agreement exists and you have collected advance rent on the basis of oral agreement,  the conditions are binding on both.

You may look into the issue and try to rectify the maintenance problem if the problem is not due to fault of the tenant. 

You may also confirm if the tenant is responsible for the reasons stated which may be due to wear and tear,  in such a situation the tenant can be held accountable for the damages to the property. 

You may try to solve the problem amicably. 

If the tenant stays for 8 months , then for remaining 4 months he can not show dissatisfaction of the property anymore.

So you have no obligation to refund the money even if he quits it before 12 months. 

Ask the tenant to wait for some more time till you get a new tenant. Take advance rent from the new tenant for a period of one year and  refund the rent for the remaining four months to your tenant.

This is purely contractual 

If you don't have the money then inform the tenant 

He can continue to use the premises for the balance license period 

If he claims that you are liable for the maintenance and since there is no satisfactory maintenance , so you are liable to refund him the pro rata license fees, then that is for him to prove in court 

However taking this matter to the court would not be prudent and would be completely unnecessary