Later British carriers would follow Implacable

Would the Royal Navy still build the Malta and Audacious classes after a delayed start to the war?

Probably not in their historical forms, because those designs reflect wartime experience that this timeline has not yet produced.

The more plausible continuation is another generation of Implacable-type fleet carriers. One existing design study added a deck-edge lift, which could appear in the next pair. That change would improve aircraft handling and enlarge the practical air-group capacity without requiring the historical Malta or Audacious design path. Later wartime experience could still lead to different large carriers after 1942.