I saw a water pump having the shaft came off while driving due to a worn-out bearing. The car was only 32000 miles old. The premature failure of water pump mostly caused by unbalanced fan or the fan belt adjusted too tight. On the older car, after a radiator flush, the water pump sometimes starts leaking. Was your water pump actually "blew up" sending pieces everywhere?
Per one of the MB service bulletins issued a while back, the engine may get very hot (I do not remember the tempurature reading) in slow traffic and it is normal as long as the cooling system is in good condition (proper mixture, pressure, coolent level, air flow, coolent flow, etc.)