Most of my good friends have returned to their own countries.
Most of the people I was close with have gone back to their own countries.
この場合、次のような言い方ができますよ。
ーMost of my good friends have returned to their own countries.
「仲の良かった友達の殆どはそれぞれの国に帰国してしまった」
ーMost of the people I was close with have gone back to their own countries.
「親しい人たちのほとんどは彼らの国に帰国してしまった」
ご参考まで!
Most of my good friends have all gone back to their home countries.
ご質問ありがとうございます。
「仲の良かった友達は殆ど[帰国](https://eikaiwa.dmm.com/uknow/questions/27105/)してしまった」は英語で「Most of my good friends have all gone back to their home countries.」という風に言えます。
ご参考になれば幸いです。