They'd both be pariahs for a considerable amount of time (decades possibly), in fact from a global point of view it might actually be better to not fire back after a limited (theatre) level attack, your opponent would destroy any credibility they had entirely.

Just the optics of the US or EU doing business with a country that lobbed a nuke at a democracy (I'm assuming it's Pakistan that fires in this scenario because honestly that is the more likely first strike, India has a firmly stated policy of no first use).

The Pakistani system is considerably more fractured and much less under control with almost parallel systems of government between the military leaders and civilian leaders.

They are pretty much the worst case scenario after NK having nukes and in some ways worse, NK doesn't have an ongoing relationship with religious fundamentalists at every level.