Irretrievable
/ˌɪrɪˈtriːvəbl/
Definition 1 of 2
Pro Tip 1/3Non-reversible Actions
Use 'irretrievable' when an action cannot be undone, often leading to serious consequences. 
After the irretrievable error, the scientific data was lost forever.
Pro Tip 2/3Finality and Loss
'Irretrievable' often implies a sense of final loss, something that cannot come back. 
The loss of the ancient artifacts is an irretrievable tragedy for the cultural community.
Pro Tip 3/3Strong Emotion
'Irretrievable' can convey strong emotions, often of regret or sorrow, about the lost item or opportunity. 
Her heirloom was irretrievably lost in the fire, leaving her heartbroken.