As for the airbag - it cannot be under the stick, of course, but there are certainly other possibilities - it can be deployed from the belt (as at some
passenger jet airbags), from the top, from the sides, or even from the suit or helmet like at some motorbike airbags. Another airbag might be used to protect the knees and feet.
As for the reliability - I believe that misfiring would be similarly critical at F1 monoposts, but airbags are used there.
On the other hand I understand that such crashes are extremely rare, and when they happen without the pilot ejecting beforehand, the conditions for survival even with airbags are slim. The deployed airbag would also seriously hinder the possibility to eject after the crash, though it is more likely that it would not be physically possible after such crash anyway.
I understand that adding the airbag may have more disadvantages than it can outweigh. I just mentioned it, because the very accident described in this thread was likely one of the cases where it would certainly help to reduce the extent of injuries.
