If the policy of the deceased person contained exclusions regarding the specific way that the person died, the insurance company may be able to deny the policy. Similarly, if the insured dies before the waiting period of the policy has been reached that policy may not be honored. But being denied a life insurance claim does not mean that your loved ones are out of luck, because you can challenge a denial, and if you can proof that the company has an obligation to pay the claim, you can be awarded the full policy value.
First, check with the insurance company to find out why the claim was denied. If it was because of an exclusion in the policy, find out what that rule is, and determine whether the deceased was in violation of the contract. The important thing is that you play an active part in the dispute rather than allowing the insurance company to deny the claim out of hand. Insurance policies are long term contracts, and there are insurance laws that prevent companies from denying claims just to avoid payment on the contract.
Provide the insurance company with any documentation you have that shows why the claim should be valid. If a clerical mistake or other error has been made by the insurance company, the denial will be overturned. If it turns out that the deceased died because of a condition that was excluded, such as suicide, then there really is not much you can do to correct the issue.
Insurance companies are not out to bilk anyone's family out of what is due, but insurance companies also fight a constant war against fraud. Because fraud is such a big problem for insurance companies, they may deny a claim until there has been time to investigate the circumstances of death or review the details of the policy. If you are not able to make progress with the insurance company, you can contact a lawyer who specializes in such claims and try to win the case with the aid of a legal expert.