I know all cancers can kill you, but which ones will definitely kill you even with treatment?

Getting fewer: If i were writing this twenty years ago, i would have listed (regardless of extent) small cell / oat cell carcinoma of the lung, alveolar rhabdomyosarcoma, glioblastoma multiforme, plasma cell myeloma, mesothelioma, and some of the famously difficult leukemias. Today, we're hearing of long-term survivals with biotech, though each of these still has a generally grim outlook.