Chuck disappeared because he graduated college and left home.
Still doesn't explain why not even his parents will acknowledge him by the end of the series.
Have you noticed that when Fonzie gets out of character or out of sorts, things go a bit haywire? This is probably because the shyer characters, like Richie, Potsie and Ralph, rely on Fonzie for advice, and when he's not available, they are random as they don't know what to do. Additionally, when Fonzie's out of sorts, the kids at Arnold's are sad. Why? Because the girls miss Fonzie as they go out with him, and because he's the only one who can start the jukebox by hitting it, so when the others have no money, they can't turn it on, and therefore have no music to dance to.
Joanie and Chachi were the only regularly appearing teenage characters whose actors were around the same age as them, thus averting the Dawson Casting trope used for the rest of the teens. This sheds light on their love dynamic.
