The average life expectancy of people in Pakistan is 66 years (rounded up). Ajmal Kasab is supposedly born in 1987 making him 23 years old. (Of course, as we have seen with Shahid Afridi, ages in Pakistan can be quite misleading). But for the moment let us assume he is 23.
He gets his sentence from the sessions court today. He can then proceed to appeal it at the High Court. After that the Supreme Court. After that the President. Legal experts optimistically put this whole exercise at about 1 year i.e. it will be at least a year before he can be hanged (assuming the sessions court give him the death penalty). An optimistic opinion mind you.
Afzal Guru is still alive.
So what are the odds that Ajmal lives his full life of 66 years? India have about 40 years to hang him.