If I was in charge I'd congratulate the guy, then seize the building and make it a rest stop for hikers and stuff. It's definitely neat enough (in my opinion) to dedicate a little bit of time to provided it's publicly accessible.
It's not on or even really near any existing trail that would make it useful as a rest stop for hikers. It's about 300m from the road up to a bunch of the most expensive houses in whister, and anybody who can find it can stop in.
There's no need to 'seize' it, just leave it as is. which is exactly what's happening - it's been sitting there for a couple years now and nobody has torn it down, seized it, vandalized it, broken it, or hurt it in any other way. It just sits there as an interesting artifact for anybody who wants to stop by and take a look.
