Less Hair
There are some open questions to what you report to have heard!
First - if that AB crew was next for departure at holding point 14L at CGN they definately would have been alighned at about 50 - 30 deg to the centre line of 14L.
I twas dark at the time of departure, therefore no chance to even have a glance on what was going on 800 - 1000 m down the runway - assume that is about the distance to achieve the necessary speed to rip of a major cowling part.
What they might have seen, if the mentioned sequence is correct, are some parts on the runway that showed up in their landing lights during t/o run.
Next was to first check if there was indeed something wrong, then collect the pieces and identify and than inform the flight.
Of course TWR could have relayed the sighting message directly to Langen center(Frankfurt ACC), running App and Dep Control for CGN, and that by simply pushing a button, activating a secured, standing line.
The same is true for the connection between Langen center(Frankfurt ACC) and Maastricht/Eurocontrol(UAC) or Eurocontrol/France (UAC)
The delay in information of the flight seems to be more related to the time needed to get factual information at hand.
Even in my "Dinosaur" times we were able to catch any "part looser" within our FIR.