罷り間違う

まかりまちがう【罷り間違う】

●まかり間違えば if bad comes to worse; if the worst happens; if things go wrong [go against one]; in case of emergency

・まかり間違えば命を落とすところだったんだぞ. Listen, man, if things'd gone wrong I would've lost my life.

・まかり間違っても even in the worst case; even if things should take the worst turn; at the worst.