CBF has been much more of a "splinter" from the SBC than a "split." At the outset, the vision was to form a group that would re-direct funding back into places where the SBC was taking it out of the CP budget, and re-directing CP giving around the executive committee. There were others, most notably the Alliance of Baptists, who were doing similar, but not exactly the same, kinds of things, organizing formally or informally, and at a lot of cross purposes. Some of the churches were more directed in their efforts, and already had a history of being at odds with the SBC, not only through the "controversy" but even before that. I was in a CBF church in Houston at the time, one in which the lion's share of designated giving went to CBF, and in which there was quite a push to sever ties altogether with the SBC. Eventually they did it, partly because they felt it was best for them, but partly to encourage other CBF supporters to do the same, partly to send the message that they wanted more from CBF in the way of a denominational identity, and partly to send a message to the SBC. Altogether, through that period of time, I think the box score on CBF churches severing ties with the SBC may have flirted with the 150 mark, out of their claimed number of supporting churches at around 1,800.
On occasion, in Virginia and North Carolina, you hear about a church here and there severing ties. But I would bet that if stats were kept, that figure would still be less than 200. If there were a push from the SBC that shoved churches off the fence, my guess, based on what I consider reasonable observation, would be that another 100, at the most, 150, churches would leave the SBC altogether. There would still be fence sitters.
People I know in CBF churches, not a lot, but a representative spectrum, tell me that CBF support is the smaller of the two, and that in most cases, those churches allow the designation out of deference to a few of their church members. The late John Baugh's former church in Houston is considered one of the core supporters of CBF in that association. But under their current pastor, for the last decade, they've become increasingly supportive of the SBC, and their CBF contribution represents less than 5% of their mission giving. They removed the notation of CBF affiliation from their website. If they had to choose, I think I could guess which way they'd go. Of course, on this board, I'd expect individuals to be in churches that, if still supporting the SBC, it's marginal. But if someone did some research overall, I think you'd find that maybe 80% of those that support CBF are the other way around, and would drop on the SBC side of the fence, if forced off their perch.