I know a lot of people are expecting that the Dungeons will be rethemed to become part of Walliams World in the next few years, but realistically I think there is a good chance that the Dungeons will be around for longer than the new area.
Whilst it would be nice if there was a more coherent master plan for the park, if anything the past few years have shown us that such a long (or even medium) term development plan is currently missing and I don't even think the park know yet what will be arriving in 2022, let alone anything much beyond that.
That said, I think the dungeons have a better life expectancy than the Walliams attractions for the simple fact that it it is not an external IP, so won't have the same yearly expenditure to pay for the rights. IP attractions are always at risk if the park ever need to slash budgets quickly - CATCF, Ice Age, Sonic, Mike the Knight and Nina and the Neurons all suspiciously disappeared at exactly the moments where the park needed to save money and arguably all of those attractions (bar maybe Nina's Science Lab) still had useful life left in them.
Obviously the future very much depends on what happens in the next few months - if Walliams World is a giant success then maybe it might have a long a fruitful future in the park, but if the public reception is lack lustre then I honestly would be surprised if the whole IP is quiet swept aside in five years - and it honestly would be difficult to remove since Gangsta Granny is the only ride with any specific theming to it.