Really? So you expect a close to 50% split then in the contributor base, and with very little overlap (few contributors to both)? If not, without this very specific outcome, I hardly see how a split could be very detrimental.
If you stepped back ~15 years, would you say to the Wikipedia folks that if they split from Nupedia, that the winner would be Britannica?
I am not claiming that you are wrong, simply that you are making a wild and bold prediction of the future as if it were a simple obvious fact. I don't believe that it is.