What could be the consequences of an untreated brief psychotic disorder?

Brief psychosis. This would depend on the nature and duration of the psychotic symptoms. If it's truly a "brief psychotic disorder, " the person has already returned to usual functioning--that's good! but, psychotic symptoms that last at least a day are best evaluated by a professional to ensure proper diagnosis and to determine whether treatment is indicated.
Need more info. Psychosis refers to a mental state where there is a loss of contact with reality. There are numerous causes for psychotic symptoms including medical conditions, psychoactive drugs and medications, etc. Need specific info plus who diagnosed you with a "psychotic disorder" or is that your thinking? Hope you'll resubmit with more details. All the best.