Supposing spleen is damaged beyond repair but not removed. What would happen to it?

Becomes fibrosed. and loses its function, the patient is considered without a spleen (asplenic) and should be managed as such, that happens to some patients with sickle cell anemia and other conditions, due to multiple infarctions they get "auto-splenectomy", asplenic patients should receive certain vaccines, be careful when they have an infection and call their doctor or start antibiotics till seeing their doctor.