Pretty good, but some things can be changed for the better...

  if ($2 == $null) { writeini away.ini $nick reason No reason. }
  if ($2 != $null) { writeini away.ini $nick reason $remove($2-,$chr(36)) }

$iif can play a big part in this, and it can be changed to

writeini away.ini $nick reason $iif($2-,$remove($v1,$chr(36)),No reason.)

In this

 msg # $nick is now away,4,0 reason: 2,0 $readini(away.ini, $nick, reason)

You can just use $remove($2-,$chr(36)) since it's still in the on TEXT event.

But overall it's good, but I prefer hash tables. 7/10