I'm trying to think what they could do with that area. I wouldn't want to remove the volcano theming on Magma as I think it looks really good and it's Paultons' first proper attempt at non-IP theming.
I think Magma would work well in Lost Kingdom but I don't think there is any space for it unless they extend the land down to Magma which I'm not sure would work.
Dealing with Cobra and Edge, I am imagining a trip to the sea side, the Edge becomes surfing the waves, Cobra becomes a pleasure beach ride with suitable 80s nostalgia music (actually you can probably come up with something better than that). The large area in front of and to the side of Edge could house a beach like Amity Beach at Thorpe Park with a paddling pool, slides, deckchairs and a kiosks serving drinks and (non-alcoholic) cocktails.
There are a few other non-themed areas they could do after that, the back of the park with the Pirate Ship, Kontiki and a few other flats and that bit at the front of the park with the log flume, chairswing and kiddie rides.
Edit: just thought, if we are going for a seaside theme then Cobra could be rethemed to Seagulls.