It looks like TfL Rail pick up the following evening relief line services from the timetable change - some still shown as working from platform 14. This seems to suggest the return of 7-car 345s on the west side for limited workings.
9N51 1727 London Paddington to Maidenhead
https://www.realtimetrains.co.uk/service/gb-nr:G91995/2021-12-15/detailed
9R59 1826 London Paddington to Reading
https://www.realtimetrains.co.uk/service/gb-nr:G92074/2021-12-15/detailed
9R63 1856 London Paddington to Reading
https://www.realtimetrains.co.uk/service/gb-nr:G92078/2021-12-15/detailed
Two diagrams
3P51 1709 Old Oak Depot to London Paddington
9N51 1727 London Paddington to Maidenhead
5N51 1804 Maidenhead to Maidenhead Reversing Sdgs
3P14 1813 Maidenhead Reversing Sdgs to London Paddington
9N14 1858 London Paddington to Maidenhead
5N14 1944 Maidenhead to Maidenhead Reversing Sdgs
5Y14 1957 Maidenhead Reversing Sdgs to Old Oak Depot
3P59 1758 Old Oak Depot to London Paddington
9R59 1826 London Paddington to Reading
5Y59 1927 Reading to Old Oak Depot
The 1856 to Reading is formed of a 9-car unit by stepping up the working which currently does 9N14 and then goes from Reading to Maidenhead Carriage Sidings.
GWR retain
1N42 1656 London Paddington to Maidenhead
https://www.realtimetrains.co.uk/service/gb-nr:L87310/2021-12-15/detailed
1R03 1756 London Paddington to Reading
https://www.realtimetrains.co.uk/service/gb-nr:L87396/2021-12-15/detailed