wouldn't they call you by ur main nick or your away nick?
anyways no real need to set global vars for the away bit maybe make use of $awymsg
example only:

On $*:text:$(/\b( $+ $me $+ | $+ $mnick $+ )\b/iS):#:{ 
  if  ($away && !$($+(%,away,$wildsite),2)) { inc -u60 $+(%,away,$wildsite)
    .notice $nick I am currently away - Reason: $awaymsg
  }
}
On *:input:#:{
  If ($1 == away && !$away) {
    haltdef
    tnick $$?="Enter your away nick"
    .Away $$?="Enter your away message"
    msg # I am currently away - Reason: $!
  }
  elseif ($1 == back && $away) {
    haltdef
    msg # I am back - Away Reason: $awaymsg ( $+ $duration($awaytime) $+ )
    mnick $mnick
    .away
  }
}