na-adjective
irreplaceable; non-substitutable; unique
Describes something that cannot be replaced or substituted, often used in formal or technical contexts. The gloss 'non-fungible' is a technical economic term.
この美術品は代替不可能な価値を持っている。
This artwork has irreplaceable value.
彼の役割は代替不可能だ。
His role is irreplaceable.
Compound of 代替 (substitution) + 不可能 (impossible). A straightforward Sino-Japanese compound.