では済まない【ではすまない】

では済まない says that a matter won't stop at a given level: the cost, the damage or the punishment will be worse than that. A noun names the level, or a verb with だけ. すむ済む is "be settled", so the phrase reads "won't be settled with just X".

The tone is serious: warnings, news reports, talk of accidents and responsibility. In speech では contracts to じゃ: じゃすまない済まない.

Usage notes

These go beyond the plain "won't stop at X".

ただでは済まない

ただではすまない済まない is a set phrase, "won't get off lightly": somebody is going to pay. Said to someone's face, it is a threat.

では済まされない

The passive ではすまされない済まされない is a judgement from outside: other people won't let the matter end there. It often follows じょうだん冗談 or a quoted excuse.

て済む問題ではない

With a verb's て-form, 済む means "settle the matter by doing", and the negative goes on the end: 〜て済む問題ではない.

ないではすまない済まない, "can't get away without doing", is a separate point.