Although my favorite place was never the tree house (neither the real tree house nor Guyser Gulch which doesn't even resemble a tree house, but is still called one although I can't figure out why), I think the real issue here is safety and not accessibility. I'm pretty sure it can't even be shored up and would simply have to be replaced. There wouldn't be anything wrong with that either, but they would have to spend millions to do it right, and they wouldn't exactly have an attraction to advertise on the front of the brochure. Not that we wouldn't like it.
How about this? Use the Waterboggan tower but build and mold a shell around it to resemble a tree. Stick some fiber optic leaves on it and call it the Four Seasons Tree House. It would be used as a great look out tower for guests, but would also light up and change colors with the seasons - shades of green for spring; oranges, reds, and yellows in the fall; and pure white in the winter. They could even provide music for it and have a light show after dark each night - mellow music, not like the Christmas tree. Of course, I still also like my miner's tree house which is around here somewhere - Rube Dugan in the trees.
Anyway, the point is, we can pretty well write off the tree house as is. You're not going to legally get inside that structure again. Now if we could only burrow into it from the roots...