Non-payment of a premium is not the same as a cancellation. For one thing, insurance companies have procedures in place, called non-Forfeiture Options, to deal with life insurance policies that miss a payment or two. For another, unpaid insurance premiums are one of the most common ways for insurance companies to find out that a policy needs to be settled. Before you get worried about the policy lapsing, call the insurance company and talk with them about your options.
A permanent life insurance policy that has been in force for a few years has another method built-in, as well. This type of life insurance policy can actually "borrow" the premium payments directly from the accrued cash value of the policy. In that way, you can miss a payment or two without losing out on the coverage.
Contact the life insurance company and talk to them about your situation. Explain that your spouse was seriously ill before passing away, and ask how you can resolve the situation. You will need to have a copy of the death certificate to prove your spouse is deceased, but rest assured that insurance companies have probably dealt with your exact situation in the past, and will know how to handle the problem. Even if the policy cancelled due to non-payment of the premium, there is a good chance that you still have a claim settlement, in the form of any cash accrued in the policy since it was first set up.
In the end, you should not have any major problems with the insurance company. Life insurance policies always come due for payment if the insured person dies, and it is not unusual for the beneficiaries to have no idea how to proceed with the claim. Just call the company and tell them that you need help resolving a policy, and they can guide you through the steps.