Natives Speakers Avoid Using 死ぬ Instead of 亡くなる
If you express “___ die”, you might use “___が死ぬ”, however, which is so direct word for native speakers and one of them may feel uncomfortable if you use “死ぬ”, instead of “亡くなる”, although using “死ぬ” is not wrong. So, let me introduce what the situations of using “死ぬ” are proper and what “亡くなる” means today!
“死ぬ” means “die” and the verb, however using “die” is a straight expression as well as English. Talking to your close friends e.g “___ died. (〇〇さんは死にました)” is fine, but don’t use it to your boss and public situations. It would be a bad impression and childish expression.
“亡くなる” means “pass away” and this is what a common word is in Japanese as well. You could use it in all of the situations in both casual and business situations. And even if you use “亡くなる” to your boss and in public situations, it would not be a bad impression rather better.
失う(usinau) / 亡くす(nakusu)
“失う” means “lose someone” which is used for especially “a car accident” or “die of one of the illness”. This expression is not too straight such as “死ぬ(die)” and it can be used to your boss and in public situations as well.
“逝く” means “gone” and these are a figurative expression. The way to use is the same as “dead” however, using it is not straight than using “dead”. Although you can say “逝く” in daily conversation, basically it is used as a written word.