May get worse. A rectocele - the rectum bulges into or out of the vagina, may or may not get worse without surgery. Ways to decrease the symptoms of a rectocele include increasing dietary fiber, preventing constipation and straining during bowel movements. Laxatives and stool softeners may also help. Weight loss in obese individuals decreases pelvic pressure. A vaginal pessary may help to decrease symptoms.
Minimal. There is very little risk with an untreated rectocele. Surgery should be based on your symptoms and how much you are bothered by them. Rectoceles can progress and worsen but this usually takes significant time and the bother issue would likely increase also so most women will know themselves when it's time for repair.
Continued symptoms. If you are not having symptoms from your rectocele then i would not have it repaired. Noone can tell you exactly what is going to happen with your rectocele. It will not just go away. It may stay just like it is or it may worsen over time. If it gets worse it can still be repaired. Their is no harm in waiting.