Ramifications of deaths of diplomats in military attack?

Imagine that Trump does nuke Pyongyang (and elsewhere in North Korea). Now in addition to many North Koreans dying, a large number of foreign diplomats will also die. How would that be treated internationally? Is it seen as a risk diplomats run? How did it operate with American diplomats in the UK and Europe in 1939-41?

Well NATO bombing of the Chinese embassy in Belgrade was not well received.

Since a declaration of war traditionally means that all diplomats of the two countries are withdrawn, any diplomats in London would have been allies of the UK. Since Germany had no diplomatic relations with those countries, diplomatic immunity would not apply.

It’d be the same for diplomats in Berlin.

I thought that in 1939-41 the US had diplomatic relations with both the UK and Germany?

Likely in Washington.

There were neutral diplomats (ie Swedes, Portuguese, etc.) in both capitals.

The outrage over the use of a nuclear weapon would far outweigh any outrage over the deaths of diplomats. The scenario you are talking about probably involves the deaths of hundreds of thousands to millions of civilians; that some number of diplomats were killed would be but the cherry on top of the United States becoming a pariah.

It would only matter in that Hillary could be blamed somehow.