Can / how do we know what death is?
'Death' happens to a 'person', 'self-entity' or 'self'.

When the mind is free from thoughts of 'self', it will know 'death' only happens to a 'self'. 

It will also know when the mind is free from 'self', there is no 'death'. 

The 'termination of life' is not the same as 'death'. 

These things the mind can know when entering into 'emptiness' (śūnyatā - 空).