Are brain infections usually fatal?

Most are not. Numerous organisms can infect brain, and typically many viral infections have good recovery, but herpes simplex may be risky. Pml associated with HIV or the drug tysabri (natalizumab) may be handled with plasmapheresis. Bacterial infections respond to antibiotics. Fungal and parasitic infections are likewise risky but can be treated. Avoid brain infections, especially abscesses, yet modern treatment helps.
No. Most are cured with antibiotics and surgery when necessary.