It sounds like you have a dual life level term life assurance policy.
This is indeed a good policy but due to the term being short on the mortgage it wont cover you both for the duration of the loan.
Your policy document will tell you for sure what type of policy it is or if you ring the insurance company and ask them for a statement, they can confirm the type of policy you have.
If you are really concerned about the short fall in the term of cover, I'd advise you to propose with another company for the same amount of cover over the term you want on a dual life basis like you have already. It may be that you can get a new policy for the term of the mortgage elsewhere. Your husband may not be able to get cover but its worth trying in my opinion as if hes in good health now then you might be able to get the cover you want.
There is good offers available from discount brokers online, google "life assurance" and a list of them will show up. It costs you nothing to propose with another company other than the time to fill a proposal form and it would put your mind at rest if you could get cover for the whole term of the mortgage.