First, its a wiki, if you want answers fast, try a forum. Steam (normally the fastest answers), reddit (notice me dev senpai! The devs are know to respond to people on this one once in a blue moon) or the PS2 forums.
Second, you don't play a lot of MMOs do you? MMOs only do auto saving, you exit when you exit, no reloading mid game.
Buildings stay untill destroyed, deconstructed by yourself or others in your squad, when the map locks or about two to three hours (I forget and will leave the fact checking to you) after you log off. Or you build over a limit of something you can only ever have so many of.
P.S. I know most of this because *wispers* it's on the wiki. Well exept the saving bit, I know that because I've played other MMOs.