After going through brain cancer treatment if it were to worsen what signs would show?

Same as before tx: If symptoms get worse it usually is the same ones that took the patient to the doctor or emergency room. Generally the cancer grows back in the same location. This is not always the case but a good generalization. Any mental status change should be looked into.

Brain cancer: When the cancer progresses, generally the cancer grows back in the same location or development of new lesion/s elsewhere. It can be presented with the same symptoms you have before the treatment -that may include- mental status change, dizziness, headaches, nausea/vomiting, gait imbalance, motoric or sensory problems- weakness/sensory problems on one side of the body, seizures etc.