Is it true a person only dies because they have a illness or disease or can some one die of nothing ?

Generally: Will in almost all cases die because of some disease process. In some respects may die of "old age" from the point of view that simply become frail but almost invariably when this happens if one looks close enough theres usually a disease process that can be found albeit sometimes not clinically apparent until death.

Death : People do doe for a reason- illness, accidents, or old age and their heart and organs “give out”.