Tachycardia rarely leads to cardiac arrest. However, everyone's risk is different dependant on many factors. Answers are rarely so simple as yes or no when talking about the human body. People should also be concerned with the potential for organ, muscle and brain damage, all dependent on individual circumstances.
SN overdose puts stress on the body as the bloods capacity to carry oxygen is decreased and decreasing. The more time since SN ingestion the less a person's blood is able to carry oxygen (to the point the ingested SN is used up). Depending on the amount taken and the length of time since it was taken a person may be able to recover or not. There is certainly a point of no return, but this is individual.
I wouldn't recommend eating it for fun or out of curiosity.