There was an accident in my friend's guild and all decorations got cleared.
Can support restore the placements?
Sorry to hear that @Mantrix.8329.
I'm 99% sure they can't: they don't save the state of the game at all, ever. The closest they come is that they take snapshots of character accounts, which allows them to "roll back" the entire account to a previous state (useful if an account was stolen, stripped, and abandoned/recovered). Apparently, it's quirky to the point that it sometimes doesn't work properly. It's also costly, in a lot of ways.
So to restore a GH, they'd have to be taking regular snapshots of every guild hall on the chance that something like this would happen and have staff trained to deal with it.
Besides, there's also the politics of it: the guild leader grants permissions to Colonel Mustard, and Mustard spams pumpkins all over. Meanwhile, Commander Clink, one of the founders objects and designs a lovely jumping puzzle, complete with "must grab air" locations for beetle racing. Mustard submits a ticket asking to restore all the pumpkins. Clink submits another asking them to restore the JP. Then Mustard submits another asking to undo that restoration Later, the body of Colonel Mustard is found in the library.
Or in other words, you can see why ANet isn't likely to create the capability to make this happen.
"With great power comes not-so-great utility bills."
I don't think so; the CS Team is hands-off when it comes to Guilds, pretty much.
The only way to find out for sure is to contact the CS Team via the 'Support' link above/below.
And I heard that when you clear decorations there is no confirmation button.
It was mistaken with a decorate button.