1 - Islam is a default religion. Aboriginal tribes, no particular one mentioned, who never came in contact with Arab merchants have been practicing Islam without knowing it.
2 - That has been so because every human being is borne with an innate religion, which, of course, happens to be Islam. An innate religion that subsequently maybe replaced with Christianity or any other religion due to environmental factors (parental influence, etc.).
3 - It is impossible to die without never having been exposed to Islam, because Allah has taken upon himself the task of revealing Islam to all those that never heard about it,
