The nukes run on a dead-man switch. If one EMP’s “everything”, the periodic “please do not launch today, sir”-signal will not reach the silos/submarines and missiles will launch automatically. We can be pretty sure that the last missiles launched will be salted with some “well, fuck you too!”-concoction to create massive fallout and maybe even some bio-weapons on top for all those weakened immune systems (from the gamma radiation). The USSR did a lot of very high quality research on biological weapons, obviously, everyone else has whatever they had in the 1980’s. People who ingest radioactive dust are goners sooner or later. Sooner with bio-weapons on top of the radiation poisoning.