Because North Korean government is a total dictatorship that has control of the press and dissent of its people could mean execution, the tragic news of the
North Korean leader's wife being executed could very possibly suppressed. That being said, if she was deceased, that news would definitely come out some time.
The North Korean leader has proven to be a wild card at every step and turn of our history. He has murdered an unknown number of people and only allows approximately 605 people in the country to use the internet. It is my opinion that it is extremely likely that he executed his wife. She need not utter more than a few words with which he takes offense in order for death to be her punishment.
Yes, she could have been executed because people get executed in North Korea for even the most minor of offenses. It does not help that she is the leader's wife. He has executed his own flesh and blood in the past. If she did anything wrong, he may have executed her.
It is unlikely the wife of North Korea's leader has been executed simply based on lack of reports of her welfare. It is widely known that the wife of Kim Jong-Un rarely makes public appearances and so the lapse of just a few months is not enough to establish suspicion of any foul play. Most media footage involving the county's highest power, typically records him making formal visits without his wife and instead surrounded by member's of his party. His wife would typically be reported to have been seen at formal state functions where her presence is generally required and to also show her support and solidarity to the regime. In the last few months there have not been such occasions.