And not just ISS but things like that are going to be only opportunity. Obviously no one will be able to continue life like before after nuking Earth. But would be a matter or who lives longer.
At the most, a thousand individuals may be able to escape from the earth in case of a nuclear war.
read the bold part in my post above again.
And what is long-term or short-term ? who sets the numbers? Even if there is no War , you wont live for eternity ,do you ? You are not long-term on earth itself. Also u dont need food and water to survive. There are meds that can keep u alive for many years,though not readily available.