Risks from Perforated Septum if Left Untreated?

Septal perforations range in size and symptoms.  Typically, posterior septal perforations can be left alone that are asymptomatic while the more anterior the perforation the more likely it will become symptomatic.  If a perforation is stable in size (especially if the patients is using nasal saline, gel and other nasal emollient) then observation is fine.  If the perforation continues to grow in size or becomes symptomatic, repair can be considered.

Septal perforations often do not require treatment. If they are small, they can be successfully repaired, but this is usually not needed. Most patients can achieve adequate nasal breathing and decreased crusting and dryness with proper nasal hygiene such as aggressive nasal saline sprays, gels, and ointments. Once the crusting and dryness is controlled, most patients are satisfied. Keep in mind that septal perforation repairs do have a relatively high failure rate, so surgery should not be the first option.
Be sure to see an expert.
All the best,

The perforated septum can be left alone but more important question is why do you have one?
It can be caused by nose picking, frequent use of OTC nasal sprays, cocaine use, rare metabolic disorders like Wegners Granulomatosis, Sarcoidosis, TB etc.
Once the medical work up is done then you need to start lubricating the nose to avoid crusting by using ary gel (OTC), saline spray and using a cool mist humidifier at night.
There is no inherent risk in leaving the perforated septum alone.
Regards