I'm not sure about this. A lot of folks are sketched out by monopharmaceutical plans. Propranolol doses over 1 gram can be lethal if you don't weigh too much. But it's not going to kill you quickly, and there's plenty of room for survival if other people will be around. You'll get super tired and pass out eventually, and probably then go into seizures and coma. Death would happen once there was enough cardiogenic shock to cause arrest.
If you take a massive amount (like 90 pills) and you survive, you may end up with cardiac issues that follow you. Best case scenario you're found and treated quickly enough to reduce long term damage.
People do attempt with beta-blockers a lot. However, cocktails seem to be more successful by and large. But I could be wrong about all of this.