What about nuclear winter? If enough nukes are launched, there could be enough ash to blot out the sun for quite a while. And this ash would likely be more nuclear fallout.
Even if half-lives are short, the damage to DNA could be irreversible. There'd be plenty of people and animals getting cancers, and plenty of deformed births which would add more to the damage. Would all of this wipe out life? No, could t wipe us all out? Possibly but we could also survive.
Also, how would the US submarines be guided around if all the electronics such as radars to guide them are gone? Who will tell the subs where to nuke?
By the way, good catch on the first wave wiping our ability to launch more nukes, I never considered the EMP blasts...
In theory, we may not even need to nuke ourselves, just nuke in the atmosphere above your enemy and let EMP disable their stuff. But then there's EMP shielding, I don't know how effective it is though.
