无人代替英文

unprecedented or unparallel these two words, basically, means "史无前例”，very close to what you've asked.

The most important, no one can replace (him/her).最重要的,无人能代替的

两个都有语法问题。如果没有人能替代你是整个句子，no one can replace you 比较准确。

no one can take it over.

irreplaceable

No one can replace you.俩选择，选择前者吧。 No one=No person.nobody强调个数.希望帮到你