Hi wendy. I am terribly sorry to hear the news of your friend. I hope he is able to make a full recovery.
I'm not familiar with the ins and outs of NCL's travel insurance. Nearly all policies cover cancellation due to illness of a passenger; many will also cover cancellation due to illness of a close, non-traveling member. Depending upon when you bought the policy, pre-existing conditions may be covered, but not necessarily so. Documentation from his doctor will be required.
I suggest that you contact your travel agent for details in this case, and for next steps. (I forget if you used a TA.) I'll also defer to others on this board who are more familiar with the policy you purchased. It was the policy that NCL offers, right?
Again, I hope all turns out well for your friend's husband.