The logical choice would be Penang, about the same distance as Langkawi, and open 24/7.
And, if you were avoiding KUL due to terrain in the area, there would be no reason to choose PEN, it has hills around as well.
Why worry about the airport being open if its an emergency? Well, for one, you would have a crash crew on duty. And KLIA would have a lot more equipment than Penang (even though PEN handles pax B-744's).