A conditional expression meaning 'if (one) could...' used to state an unlikely or hypothetical wish/possibility.
戻れるものなら、あの頃に戻りたい。
If I could go back, I'd like to return to those days.
行けるものなら今すぐ旅行に出たいが、仕事がある。
If I could, I'd go on a trip right now, but I have work.
助けられるものなら、誰でも助けたい。
If one could help, they'd want to help anyone.
A conditional used to warn that if someone were to do X, an unpleasant result would follow (often used as a strong warning; typically appears as verb stem + ものなら).
そんなことをしたものなら、二度と許さない。
If you ever did something like that, I would never forgive you.
親にばれたものなら、厳しい叱責が待っているだろう。
If your parents found out, a severe scolding would be waiting.
彼に本当のことを言ったものなら、関係が壊れるかもしれない。
If I told him the truth, our relationship might be ruined.