Subs aren't made for first strikes. The point of them is to hide and launch their nukes to enforce the MAD doctrine. the important parts of the oceans near the US and Russia are guarded quite well even according to publicly available information.

I can't really predict or imagine what would happen in the event NYC was hit with a nuclear missile, but my gut says we'll be back to sticks and stones, regardless of who launched it. A bomb could be blamed on terrorists. Not an ICBM.