The latest information is that the bustitution will be running from Lord Street.
From http://www.examiner.co.uk/news/no-trains-huddersfield-dewsbury-1-13352956
It's about 300m away from the station, but I guess as nothing will be running through the station interchange with trains is not an issue. Keeping the RRBs well away from the Food Festival is probably for the best.
Will there be provision for taxis at Lord St though?
The walk from there to the Bus Station could be quite challenge, especially with heavy luggage.
Back in the day in the 1960s, before the new bus station was built, Lord St used to be used as a terminus for long-distance coach services, originally Yorkshire Traction, then National Express, to London and other cities.
What goes around comes around.