What would happen if anemia goes untreated for 6 months?

It depends on... Mild anemia may cause no symptoms so if untreated it would not have any particular consequences. More severe anemia may include fatigue, weakness, shortness of breath, fast heart rate, headache, cognitive problems etc. so if it goes untreated you would suffer with those symptoms until corrected. But this should not affect your ability to respond to proper treatment.
Gets worse. Depending on the type of anemia, symptoms could get worse. Most types are easily treated so no need to wait 6 months.