がここにいない

is not here

→ が
phrase Common #3,560
is not here The subject before が is the person or thing that is not here. The provided examples use the related phrase がここにいる, meaning “is here.”
JA: 田中さんがここにいないので、後で電話しましょう。
EN: Tanaka isn't here, so let's call later.

トムがここにいないとかほんとビックリ

I’m really surprised Tom isn’t here.

トムメアリーがここにいない理由を知りたがっている

Tom wants to know why Mary isn't here.

がここにいないのは変だと思いませんか

Don't you think it's strange that he's not here?

私の友人がここにいないのは残念だ

It's a shame that my friend isn't here.

がここにいない寂しい

I feel lonely when you're not here.

彼女がここにいないのが残念だ

It's a shame she's not here.