With the exception of sandbags, nothing they’re doing will be noticable in 20 years, the only bits of the older stuff that are recognisibly “altered” or “vandalised” or whatever are the bits that still get ridden. Apparently there’s a commitment to remove all sandbags and structures when the “zone” gets retired but inevitably some’ll be missed or impractical to remove. There’s a lot more digging and “damage” than there used to be but it’s still an absolute flyspec.
So I think it more or less comes down to whether you think there’s something sacred about the exact shape it was before, but the whole landscape is a product of constant erosion, so equally if you don’t build trails then come back in 20 years it’ll also not be the same as it was before.
(as an interesting side effect, the old Rampage site, which is state owned, was put up for sale and had oil and gas drilling licences granted. Both the sale and the licences were subsequently cancelled and mountain bikers were given a large part of the credit for that- they were both the largest body of protests, and also helped raise awareness and funds to support the local communities in their own actions)