Totally depends.
If its features you built in a location that could be turned into a terrain park, sometimes they leave it. PCMR turned that slopestyle course into their expert king's crown park for example. If the features are too big, sometimes they'll take down a bit of the gnarly stuff, push takeoffs forward a bit and leave it as a park.
Of course, if you had to run the event somewhere else, you just totally plow it down and get rid of it. When I used to work at Blue Mountain and we did the Triple Challenge village big air, that thing was ripped down immediately upon completion of the event.
This is a big reason really cool events come at such a high cost. Grooming time runs about $200 / hour, and lots of times the mountain doesn't get to keep the really massive / custom stuff.