At the same time though, this kind of thing is the best sort of learning. Take your assumptions and make a theoretical model, go out and test it, and learn first hand what elements you didn't account for.

My opinion is that once your kids hit a certain age, your role is more support and providing guidance to avoid/recover from really bad outcomes (see: if your son's plan had a flaw that would've left them stranded. They made it there and back, if exhausted and slightly [but from the sound of it not unrecoverably] poorer. Shitty, but they probably learned some valuble lessons.)

Edit: This may just be copium from my own "I'm gonna move to the middle of a different province with my homies" adventure that left me with just enough cash for a bus ticket to supportive family if I survived on Corn Flakes for two weeks. Ah, to be 19 and know everything again...fuck that would suck.