unreplaceable

/ˌʌnrɪˈpleɪsəbəl/
adjective
  1. Not able to be replaced; so valuable or unique that nothing or no one can take its place.
    • Some antique car parts are unreplaceable, making restoration very difficult.
    • To the team, their captain was unreplaceable because of her leadership and experience.
    • The old photograph was irreplaceable, so she kept it in a fireproof safe.