Whatever happens to him? I am just now getting to Season 3 and he just left to go to college in Chicago. I know he dies eventually in a lter season, but does he and Mary ever get back to each other? How is she affected by his death? How does he die?

Supposedly, someone killed him (Season 8, "Chicago"). He had supposedly cheated on Mary earlier, and they never got back together. By Season 8, Melissa Sue Anderson had left the series, so I don't know if Mary was ever told and how she took it. I guess that's up to us to imagine!!

Radames Pera (John Jr.) attended a Little House event in Nebraska last month, along with fellow cast members Karen Grassle (Caroline), Charlotte Stewart (Miss Beadle), Alison Arngrim (Nellie Oleson), Brenda & Wendi Turnbaugh (Grace), and Brian Part (Carl).

http://www.youtube.com/watch?v=kVH2JKkG7Zo