His loss of coverage is a Special Enrollment event (under HIPAA Portability rules). As such, he is allowed to enroll for coverage for both himself and his spouse. There is an exception if your health plan (1) requires an employee declining coverage to state in writing the reason for declining coverage is the existence of other coverage and (2) at or before the time the employee declined coverage, the employee is provided with notice of the requirement to provide the statement (and the consequences of the employee's failure to provide the statement), and the employee does not provide the statement. In that case the employee's request to add the spouse could be refused.