Hi dm,
ESA is actually an open-ended award that will continue to be paid until/unless a new decision changes the award. Any review date is only advisory. There has been a large backlog of cases and DWP has actually suspended ESA reassessments for 2 years in many areas. The only way to know whether your hubbie is due to be reassessed soon would be to phone DWP and ask, this would not trigger a reassessment. However, even if you were told, for instance, that reassessment was due next year, you still would not know whether it would be further delayed!
Nothing on this board constitutes legal advice - always consult a professional about specific problems