Is the waiting period (iddah) obligatory for a wife after the death of her husband who had ceased contact with her but did not divorce her?

If a divorce has not occurred by the time of the husband's death, the wife must observe the 'iddah (waiting period) of death (four months and ten days) if she is not pregnant. The same applies if a revocable divorce occurred and the 'iddah has not yet expired. However, if he divorced her and her 'iddah has expired, she is not required to observe the 'iddah of death upon his passing.