Who really knows why he did say goodbye at that time,maybe he thought it would be better to just go,and wait if i recall correctly he did say bye while jumping on shenrons head.And when goku and vegeta jr were fighting,he could have not seen pan,didnt want pan to be nuts telling everyone she saw goku,(they may not beileve her and think she is going nuts missing,and imagined him.)Or maybe he thought it would be best if he just left unnoticed.The thing i dont get is that he is a very famous person at that arena and nobody noticed him.answer me this plz,goku jr. is pans grand son rite,vegeta jr.is who's son,and who was that who spoke with pan that could not have been bolma she is older than pan.My guess is goku jr. is goku's great grandson and vegeta jr. is vegeta's great great grandson,(1 last thing was it me or was vegeta jr voice a bit deep for a kid,i no he is vegetas kid but still a bit deep and raspy for his age.