They branched off exactly because they saw Mandriva was failing, and they wanted to make sure the distribution wasn't dependent on such an unstable company. With Mandriva S. A. giving more things to the community, it would be interesting to see both merge again ("Mandragora Linux"?

). But Mageia is still a good project regardless. Their distribution is still small, but that's why it feels very "cozy", developers are being helpful and willing to provide help (and receive help in terms of packaging and such). Oh, and they actually provide a good variety of LiveCDs, with free software.
Also, since when do Linux distributions need a reason for existing? :P