それが本当なら

if that's true

→ 其れ
phrase Uncommon #17,887
if that's true Used to introduce a condition based on something being true. なら means “if” or “assuming that.”
JA: それが本当なら、すぐに知らせてください。
EN: If that's true, please let me know right away.

それが本当なら首をやる

If that’s true, I’ll cut off my own head.

もしそれが本当なら中川有罪であるということになる

If that is true, it means that Nakagawa is guilty.

それが本当なら彼は事故を起こしていない

If that's true, he didn't cause the accident.