They do want the boys on the B list - they wouldn't be on the B list otherwise. It is absolutely expected that up to half the boys on this list will eventually get a place because of last minute changes of mind.
A couple of schools have already closed completely, and I'm sure there will be more, however I don't think it will affect Eton one jot. It will affect the parents who are just about affording it - and several do make huge sacrifices to send boys there. It may slightly reduce the bursary pot too.
It will be interesting to see how this all pans out, and whose predictions will turn out to be correct - will it cost more than it raises, or will it pay for thousands more teachers?
I think this will just be hugely unpopular with parents but ultimately they will blame Labour, not the schools.