A person can die of pneumonia.
Tribes, tribal customs, and populations can die out.
Just take a look at the diferences in the results that Google gives you for the two phrases:
die of - http://www.google.com/search?sourcei...q=%22die+of%22
die out - http://www.google.com/search?hl=en&l...=%22die+out%22
I hope that helps.
- For Teachers