1A 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.
2A 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.