C.M., I can only comment on the procedures in MUC as a CDM- Airport.
First we have to clear up a common misunderstanding. The CTOT is the time the aircraft has to be at the runway.
The slot window -5/+ 10 is a time for ATC only, to handle flights with a CTOT more flexible (for example those unforeseen circumstances you mentioned)
But in reality this slot window is often used by the airline to compensate the delay they have and to avoid a delay message ( or a new target offblock time
at a CDM airport).
If an aircraft missed the slot during taxi we generate an updated target take off time which triggers a new CTOT. ( CDM airports have a automatic data exchange
with the NMOC in Brussels ). If we are not pleased with the received CTOT we call NMOC on landline and ask for improvement. Of course there are sometimes regulations that cannot be improved. Then the flight will stay close to the runway and if necessary shut down the engines there. However this worst-case-scenario
is extremely rare.
By the way, flights with a urgent slot will prioritized if circumstances permit. Unfortunately in the last weeks/months almost every flight had a slot and this
makes it a lot harder to save the day for the urgent ones.