Well, that is a waste of INI for a simple task like this. This script should have used a local variable, and that's more than enough. Here is my version:

on !*:quit:{
  var %c = 1
  while ($comchan($nick,%c)) {
    if (,$+(%,$wildsite,..,$network,..,$v1)) {
      unset $v1
      inc %c
    }
  }
}
on !*:part:#: if (,$+(%,$wildsite,..,$network,..,#)) unset $v1
on $*:text:/^b(rb|ack)( |$)/iS:#:{
  var %b = tokenize 32 $!($+(%,$wildsite,..,$network,..,#),2)
  if ([ [ %b ] ]) { | if ($regml(1) == rb) {
      set $+(%,$wildsite,..,$network,..,#) $nick $iif($2,$2-,None.)
      [ [ %b ] ] | .msg # » $1 will be right $&
        back. Reason: $2- « | return
    }
    [ [ %b ] ] | .msg # » $1 is back from: $2- $+ . « 
    unset $+(%,$wildsite,..,$network,..,#)
  }
}