Grounds for lease termination?

A lease is a contract and there are several grounds on which a contract can be voided.  One of them is lack of mental capacity. 

If a person is found to have lacked mental capacity the contract cannot be enforced.  For instance, very small children may not be held to bargains they have made, on the assumption that they lack the maturity to understand what they are doing.  Another example might be people who are mentally incapacitated, either by disability or drunkenness. When the law limits or bars a person from engaging in specified activities, any agreements or contracts to do so are either voidable or void.

Typically, a finding of incapacity is not readily made.  Depending on the severity of your husband's condition (and any medications that he was taking) such a finding may be possible.  But it may well will be a difficult case to argue.

You should consult further with an attorney in your area as to this.