Not a problem on the celica, since the only available side-impact airbags on the celica are optional, and located in the side bolster on the seat itself. (hence why they are called "Supplimental side-impact" and not "side curtain". Side curtains roll down from the top, not like on the celica)
How many people have the side airbags on their celica anyway? I know mine doesn't have them.
Either way, I wouldn't worry man, I don't think you drilled into your airbag there, maybe something else (like a wiring harness, which is why you should be careful, don't want any shorts in the wiring now...) If the airbag itself is punctured, it may tear when inflated, depending on where he poked a hole in it, and how much force it deploys with. Of course, there's also the issue of a sharp screw now sticking in the airbag, which may tear the airbag when it deploys, or if the airbag works, it may just drive that sharp screw into your head when you get into an accident.
In the future, just remove the factory pillar plastic (it just pulls off) Use masking tape to attatch the factory pillar to the back of your new pod and keep it alligned, then, at a workbench or a milk crate, etc... Drill out your holes through both pieces, and then use the supplied rivets or screws to attach the pod to the pillar. Don't forget to drill a hole in the factory pillar big enough for all your wires, pressure lines, etc before attaching the pillar to the pod. You can also line up the pod to where you want with the pillar still inthe car, then use chalk, crayon or china marker to mark the position of the pod on the pillar, then remove the pillar plastic and mount it as I mentioned above.
Look at the bright side, at least the mistake of one person will help others not to make the same mistake when they do a similar install.
Some pods are full replacement, so, no drilling, screws or cutting, it just presses up in place of the factory pillar plastic.
BTW, a hammer and nail is NOT the right way to make a proper hole in the pillar pod, I'm shocked that you didn't crack your pod doing it like that.
READ THE INSTRUCTIONS! they'll tell you WHERE to drill, What size bit to use, and HOW to fasten the pod to the pillar (Mine used four plastic ribbed rivets, similar to the ones that are used to fasten door panels)
Did you unhook your battery for this install? if not, count yourself lucky, since wiring harnesses, and a windshield fluid tube for the rear window are run under that pillar plastic on the celicas... Can you say ZAP?!? God only knows what possible wires or other bits are under the pillar on your car (you already mentioned the airbag, that may not be the only thing)
JettaMan, honestly, if I were in your current position, I'd pull those screws/nails/whatever is holding the pod on, pull the pillar plastic off, and double check those harnesses underneath to see if you cut a wire's insulation, or poked a hole in the hose under there, just to be safe. As for your airbag, I just hope nobody t-bones your car, because now, I'd say you have a 50-50 chance it will work as intended.
Good luck man