I am sorry to hear of your dilemma. I realize how frustrating this is for you and I hope to provide you information which is accurate and useful, even though it may not be the news you were hoping to get.
Unfortunately, your son's lease is binding and enforceable for the lease term stated in the contract. Therefore, without a provision in the lease providing a right to early termination or landlord breach (constituting constructive eviction), he is liable for the payment of rent and other obligations specified in the agreement until the end of the lease term.
So, he has a few options. First, he can try to find a new tenant to either be a subtenant or assignee of his lease.
Next he can try to negotiate a lump-sum settlement of the remaining balance on the lease.
Finally, and most risky, he can just move out without a new tenant or settlement, and hope the landlord can relet the space quickly.
The last option puts him in breach of the lease and subject to damages if the landlord sues and prevails.
With regard to the first two options, if you find a new tenant or reach a settlement with the landlord, it is most important that the terms be in writing and signed by the parties so that it is enforceable in court.
Also, be aware that the landlord does have a legal duty to mitigate damages if your son moves out.