I think the prep week was to titrate the ideal drug cocktail more than anything else. The one they used for the SOTU has him slurring and talking at 3x speed out of the gate, but crashing well before 90 minutes. They clearly went with a more middle of the road mix with the disastrous results we all observed.
With no teleprompter and having to recall facts and string together coherent thoughts for a full 90 minutes it is beyond what drugs can help with at his stage of dementia.
They absolutely had to know this going in. Canceling the debate at the 11th hour would cause less damage than putting him out there did. Yet they did it anyway.