CR taking the rights to translate this manga will make the fan-translation groups to drop it?
Very possible, but not necessarily. Though I can't speak for either of them (how many groups are actually scanlating this? at least two, right?).
Some groups have indeed dropped scanlations on a number of titles that CR has licensed, and like, on the spot too.........while others haven't. Manga Stream, at least, is continuing to scanlate a number of CR titles. I don't have a clue what either the people scanlating under No Group or Futari wa will do. At least in the case of Futari wa Pretty Anon they haven't made any type of announcement on their site about it yet, and I've no doubt they saw the announcement about CR starting it too.