While agree that various points raised are valid, I also think that there is not much value in discussing details without more input or partipation from the OP. We really don’t know this family or what prompted the sudden decision to “go west.” So I don’t think it’s valuable to insult the kid or overdramatize. The parents are going to figure out soon enough what is going on and what prompted the sudden decision to pull up stakes and leave.
I agree that it’s unfortunate that parents are expected to pick up the mess … if either of my kids had done that, their “stuff” would have been long gone, because as a parent I don’t run a moving & hauling service. But then again, the “stuff” really doesn’t matter much anyway. My son was more proactive in shipping stuff back home before he quit college, including new acquisitions like a ginormous computer monitor – and all that stuff ended up sitting in his old bedroom forever after that, except for the stuf that I’ve managed to clear out and give to goodwill or the e-recyclers over the years. If the kid doesn’t want/need the stuff now, odds are he never will.