Honest answer.... my guess, and I'm basing it on Europe, would be about 70%, in the States don't really know, I have about 50 buddies on the list I write with, but all of them are mature strong believers so for them 100%.
In reality God seems to have hidden His 'remnant' amongst all the 33,000 denominations that man has created, and the reason is that when Mark & Cº get stronger, and as the AC starts up, being hidden amongst a whole lot of pew warmers will be a safe way to stay alive when the real persecution starts, so there are a whole heap of people out there who have been going through the motions and singing their hallelujahs, paying their tithes and doing their good deeds, but they still are not actually 'sold out' to Christ.
Then there are those who are hidden and will stay that way, though it seems we are now near enough to the end for the cry "Come out of her my people" to be shouted from the rooftops.
I was asked to preach at a church once and had no subject until I got there (I'd been asked a month before) when God said, preach on OSAS, so I did, I preached a safe preach in a safe church of older people who had been Praising the Lord for longer than I had been out of diapers, and the preach was:
"I believe in Once Saved Always Saved"
Relief big time from all the elders....
"But the emphasis is in the word 'ONCE'..."
Then I outlined what Christ sets out to be the standard for 'knowing' Him and asked "Do you fit the bill"
Pandemonium and it took 20 minutes for the mob to die down, the pastor (who was alive) told me it took him two weeks to explain what I meant and to calm things down.
So you tell me, how many do you think would be shaken out of their beliefs?
Dawkins is very logical, but then so am I, and I did get to a point about one third through when I was asking God "Why am I reading this?" - and then I found out why and had the antidote to his premises that will set any real believer back on course, or advise a pew warmer how best to make his exit and start enjoying what life he has left before the end.
My theory, if you are a Christian because you fear Hell, you're probably lost anyway... I changed teams because I saw that God won and it's no fun being with the losers, even if they do get all the glory here on earth.
Besides which I had gotten a little too deeply involved with the other team and I became aware that I had demons on my back, so I wanted to get free from them NOW, like whilst I'm alive, because they were problematic enough here and now, so I did not want to face any afterlife in their presence.... if you see what I mean!
Anyhow, there's a hub hers so I'll stop and you can read more if you want to when it's posted!