Prognosis depends on particular tooth, the extent of bone destroyed & accessibility for treatment.
1) Carcinomatous/Neoplastic Changes:-
Squamous Cell Carcinoma or Epidermoid Carcinoma may occasionally arise from epithelial lining of Radicular Cyst.
2) Pathologic Jaw Fracture:-
If Cyst have completely eroded the bone specially if it is present in posterior region which is very rare in case of Radicular Cyst it may cause pathologic jaw bone fracture.
3) Secodary Infection:-
Cyst may get secondarily infected and create further complications.