YOU SAID:

It is so cool that he is not coming to the party

INTO JAPANESE

彼がパーティーに来ていないのはとても涼しい

BACK INTO ENGLISH

It is very cool that he did not come to the party

INTO JAPANESE

彼がパーティーに来なかったことはとても涼しい

BACK INTO ENGLISH

It is very cool that he did not come to the party