What usually happens if a minor cross bite is not fixed?

Depends: It depends on the person. Factors include age, how sever, what the cause is and more. Sometimes it can cause problems in the future such as chipping of teeth, cause the jaw to bite to the side, cause teeth to wear down quicker than normal. Ask the dentist if you are at risk for any of these.

What is minor x-bite: In a child, the jaw is growing and a cross bite causes the jaw joint (tm j) to grow asymmetrically. Once the growth is complete it is too late to fix. Later, as adults, these people begin to show symptoms such as painful tm joint, clicking with opening and closing, headaches to name a few. If at all possible, a cross bite should be corrected. Ideal age is around 5-6 yrs. When cooperation begins.

What's minor?: If there's a cross bite, or an overbite, or an underbite, or crowding, or rotations, or any irregularity, it may be only part of an overall malocclusion. When there is one eruption anomaly there are often multiple eruption anomalies. See an orthodontist for diagnosis and treatment planning. If untreated may lead to uneven wear, supporting tissue damage, alteration in jaw growth, etc.