The Clow Card love the one who sealed them off the most, thus, the didn't excactly lose their memories; the forgot about the one the loved so that they wouldn't get hurt (in Cardcaptors, however, they just had everyone forget about anything related to the Cards instead of their loved ones).
However, Kero states in the manga that the disaster depends on the cardcaptor personality. The anime doesn't point this out too clearly, but I remember that there was at the end of one episode (I'll check which one later) where Sakura asked Kero about the disaster and he told her that it wouldn't be something like the end of the world. But then, when a relieved Sakura left, we heard him think "but depending on who you are, it could be far worse than the end of the world...". Ehh, hope you followed me there.