Like others, I think the appeal with be successful and the decision of the lower court (the High Court) will be overturned. I think the basis for the overturning will be that the case was a judicial review and the lower court got drawn into thinking about right and wrong when they should have been considering whether the practice of the Tavistock was legal.
If I've guessed correctly, and I hope I haven't, there'll be huge celebrations by trans activists, Maugham will be intolerable, but after the party when they see where things stand, and when their demands for things to return to how they were end up being ignored, they'll realise that this wasn't about what a court decided but was about professionals being reminded of their responsibilities, in the context of growing public awareness, and exposure to sunlight. This genie won't be fitting back neatly into the bottle.