Is the Umrah waived for someone who entered into a state of Ihram with the intention of performing Umrah, then exited that state due to a dispute with his brother and returned to his city without completing the Umrah, and then passed away?

The state of ihram for Umrah is established by intention alone. So, if one intends to enter into Umrah, he is in a state of ihram, and he must complete it; it is not permissible to abandon it. If a person in ihram for Umrah passes away, it is not legislated to perform it on his behalf to complete it. However, if it was an obligatory Umrah (i.e., Umrat al-Islam) upon him and he did not perform it, then the cost for someone to perform Umrah on his behalf must be taken from his estate before its distribution. It is also permissible for someone to voluntarily perform Umrah on his behalf.