That pretty much.
Nuclear weapons are detergent. Nothing more, nothing less. Chances of them ever being used by a non-religious government are close to non.
Independent terrorist groups are another story though.
Sorry, I know this is a language thing, but I laughed so much when I read that, I think you mean deterrent, detergent is something like soap that you use to clean things with which, one could argue, something a nuclear weapon could do.
On the actual subject, if one country were to fire a nuke, another country would mostly retaliate on that country with another nuke. Israel isn't just gonna start firing off nukes for the hell of it, it'll be (if at all - I consider unlikely due to the ramifications of firing a nuclear missile) in retaliation to something another country does. From there, who knows what will happen, depending on the circumstances, you can't say USA won't defend Israel, from there the other Arab nations will probably join forces to fight USA, USA calls in its allies from Europe/Asia and it's world war.
All that said, I don't think any of this will happen. Nuclear war and the end of the world has been predicted since the first bomb was dropped. There's a reason USA and USSR never fired on each other, simply because they knew the other country would fire back. In today's day and age with early warning missile detection, you can believe that the country you fire upon will have fired back before your bomb hits.