Are you planning to die? We all will someday and its not entirely in our control when. Death in Service benefit through work can “pay off” the mortgage so the other parent has somewhat less worries. Depending on the multiples etc, there may even be a small surplus – but a grieving family can consume money very quickly. Having been pretty close to such a situation I can assure you it would have been far better if there was proper life cover too, then the surviving partner (and children) could have been quite comfortable for the future, rather than just not badly off. Its also worth considering that if you get a very serious illness you may end up no longer working (and thus not being “in Service”) before death, but will by then be likely uninsurable.
Critical illness cover is harder to answer in my opinion, as they become increasingly difficult to extract payments from.