A helmet can save your life. Other armour, an airbag, gear in general will probably reduce road rash, soft tissue injuries, maybe preserve the odd bone. All dependant on the circumstances of the accident, the speed, what you hit, how you land etc. etc. There are no guarantees. IMO, gear is always better than none and I'll continue to wear it.
I was having a coffee in a small town on a back road and there were 3 super sport riders there at another table discussing the pros and cons of leather vs. textile. The leather guy maintained that in a 100 kph collision with a car that he would have fewer injuries that the guys in textile gear. I thought he was joking, but not so, they argued for a while as to who would be less injured. No one asked for my opinion, sitting a few tables over with textile gear, and I didn't offer it. Obviously these guys were completely delusional about protective qualities of the gear they were wearing.