وَالْأَجَلُ وَاحِدٌ
The appointed term is one.
The account does not posit two distinct actual appointed death-times for a person, one if killed and another otherwise. Some historical philosophical explanations distinguished natural death through the exhaustion of bodily moisture and heat from accidental death through illness or injury.
These are historical physiological theories, not substitutes for modern medicine. The theological conclusion is that natural or accidental causes do not independently revise the actual time of death known to Allah.