I’ve tried reasonably hard to collapse a keg over a period of years. It might well be possible, but I haven’t managed it.
Ok, I wasn’t actually trying to collapse them. I was filtering, but you get the idea.
@BrotanicalMatt tried a 35cfm Edwards on one, and also failed. I don’t know that he took it down to 1um and then started beating it with a broomstick, but I believe he gave the pump a reasonable shot at collapsing the keg.