Tenant Request To Vacate Early

[CJ B.]

Hello, 

Would like to know how others handle this situation— 4 year tenant, has paid rent on time, suddenly requests an early vacate. It’s December, lease is up in May. They tell me theywon’t be able to pay as he was in a car accident and needs to vacate to live with a relative.
 Very difficult to rent in winter months . It’s out of state.

What is the optimal strategy for this situation?

I do have an early termination clause in the lease. But how does one enforce this, if at all? 

Thanks!