The key word here is “exclusions.” If the policy has an exclusion for a certain type of death, then they don’t have to pay. The good news is: There are usually not many exclusions. Different policies have different exclusions so it’s best to read the policy or at least ask. Group policies usually have more exclusions than privately purchased policies.
Suicide and lying on the insurance application are two common exclusions; however, they usually disappear after two years. Some other exclusions may include: dying as a result of an act of war, dying in the commission of a felony, or committing fraud against the insurance company (by insuring someone and murdering him, for example.)
It is standard for insurance policies to have a two year contestable period after which it will pay for almost any death. During the two year contestable period they will not pay for suicide or if there are substantial misrepresentations on your insurance application, but these exclusions disappear after the two-year contestable period is over.