Yes, Basal Cell Carcinoma can kill if left untreated.
Basal cell carcinoma is rarely fatal (less than 0.1% of patient deaths due to cancer) and rarely spreads to other parts of the body, but if left untreated it can damage vital organs, bones, and blood vessels.
A 44 year old male who lived alone on a farm and suffered an injury 2 years previously, growing lesion for 10 months. For full history see: Neglected Basal Cell Carcinomas in the 21st Century