Should I tell my ex's family that he's decided to become a "drifter"?

I met with my ex for a final dinner tonight (I'm moving) and he seemed more mentally unstable than usual. He told me that he's been sleeping on the beach even though he has a perfectly fine apartment because he feels "uncomfortable" there. So he's moving out so he can live on the beach and crash at acquaintances' apartments for who knows how long. I asked if he was going to tell his parents (with whom he speaks every week because they demand that he do so) and he said no. I've never talked to them at all but I feel like I should somehow try to get in touch with them and tell them what's up. Yes, he's an adult, but he's only 23 and he doesn't have any friends here to make sure that he's OK after I leave. What to do??