The legal relationship resulting from a divorce can vary depending on the jurisdiction and the specific laws that govern family relationships in that area. However, in most cases, a divorce does not affect the family relationship of the non-biological line partner with their former spouse's family.
In the scenario you described, if your aunt and uncle got divorced, your uncle would still be your uncle by law and by the familial relationship that was established during their marriage. Divorce dissolves the legal bond of marriage between two individuals, but it does not automatically sever the familial relationships that were formed during the marriage.
The term "uncle" is commonly used to refer to a parent's brother, whether through blood or through marriage. Since your aunt was your mother's sister, her ex-husband would still retain the title of "uncle" in relation to you, even after the divorce. He would continue to be your mother's former brother-in-law and would maintain a family connection with your mother's side of the family, unless some other legal action were taken to sever that relationship.
It's important to note that family dynamics can be complex and vary from one family to another, so individual preferences and circumstances may influence how family members choose to maintain or redefine relationships after a divorce. However, from a legal standpoint, divorce generally does not erase family relationships established during the marriage.