the scott contessa's rear der. hanger is not replaceable, but Scott offers an amazing "crash replacement program" where if you crash your bike or the der hanger brakes and it is your fault, they will sell you a new frame for less than wholesale.
my advice is to test ride both of those bikes and get whichever one feels best to you. both scott and cannondale make great bikes. for me i have found i like the contessa better. in the smaller sizes the cannondale seems to beat me up and be too stiff. when i ride a cannondale, it feels like my fillings are going to fall out.