You ignored the reply that I made to your last post - the drivers do self dispatch, unless the station has been assessed as unsuitable (i.e. unsafe) to do so. That means somebody is required on the platform. For obvious reasons, the driver cannot be on the platform as the train is departing.....
The way to sort this would be to train staff such as booking office with dispatch competency to cover as a contingency if nobody else is available.
Yes drivers and guards both do self dispatch where the risk assessment deems it acceptable.
When you start getting into which roles can cover be trained to cover which starts to get a bit messy.
The dispatchers I know of (it may not be the same everywhere) are PTS trained and have a competency cycle, just as other safety critical staff such as drivers, guards and signallers all do.
Having booking office staff covering once in a blue moon is a recipe for disaster and frankly many staff would not be willing to put themselves in such a position and certainly not for additional pay for the additional responsibilities.
If it was tried I have not doubt the staff would be bringing it up at union meetings and saying it’s unacceptable.