You know this, I'm sure, so this is for everyone else as much as you: document the shit out of the damage - photos, phone logs, take notes of conversations including dates and times, etc. - and if you can do it cheaply and quickly, get an estimate on what the damage might be to fix. Hold this through the next four days. If they take possession cleanly, there's no real damage and you can chalk this up as a great story about a pack of assholes that you got one over on (seriously). If they try ANY last minute bullshit, renegotiations, or games with the closing, BAM, you have the Hammer of Thor to throw if you need it.
I'll tell you what though; f*** people. There's no honor or decorum anymore. And while you are closer and have more insight than I do, I don't sense it was malicious as much as it is just stupid and inconsiderate, but still. I grew up with the notion that someone's house was a sacred thing; the most expensive thing that most people would ever buy, and the place they put their families and their LIVES. Now? It's a set on a shitty reno show on HGTV. (Not to veer off on too much of a tangent, but you ever notice that? On those renovation shows like Property Brothers, people go into other people's houses and make the most rude and disparaging comments. I might THINK it, but as Daryl Hall once said, "some things are better left unsaid." Those are people's HOMES.)