I think Wilt's 50.4 PPG is the least likely to be broken. The 100 point game would be near impossible to break to, but I think since Kobe scored 81 people have realized it might be possible, though still very unlikely.
50.4 PPG is just insane though. The NBA is not fast paced enough for anyone to come close to that again. How many players have even averaged over 32 PPG in the last 15 years? The only two seasons that come to mind are McGrady with 32.1 PPG in 01-02 I believe, and Kobe's ~35 PPG in I think 05-06. 50.4 for a season is just impossible in this age, even a ball hog/chucker of Kobe or Iverson's caliber couldn't even come close to that.
It would take a completely dominant center in the mold of Wilt to even have a shot at it (he'd have to be a hell of a free throw shooter too), a wing player couldn't do it in this age. It's extremely unlikely we'll ever seen a big man that far ahead of his peers in terms of size, strength and ability again.
The rebounding records from the 60s are just as unbreakable due to the changes in pace and shot attempts in subsequent decades, but I've always been amazed by the 50.4 PPG season. Just an incredible record.