となったら

expression

when it comes to; if it becomes; where ... is concerned

Used to set up a hypothetical or conditional situation, often followed by a statement about what would happen or what one would do in that case. Can be translated as 'when it comes to...', 'if it becomes...', or 'where ... is concerned' depending on context.

• いざとなったら、私わたしが責せき任にんを取とります。

  When it comes down to it, I'll take responsibility.

• 彼かれが来こないとなったら、計けい画かくを変へん更こうしなければならない。

  If it turns out he's not coming, we'll have to change the plan.