The use of a given weapon is only considered to be "unthinkable" until it's been done (or in the case of atomic weapons...done again, since the USA already used then in 1945). Then all bets are off.



The ONLY acceptable response, other than unconditional surrender, to a nuclear attack is an overwhelming destruction of the attacking country, and all of it's active supporters- Otherwise, the world community has made it clear that the use of such weapons would be acceptable, and they will continue to be used.