Nonborn, there is no # in the quit event. You can combine all the text events into one:

on 1:quit:delete
on 1:part:#:delete
alias -l delete {
  if ($read(awaynames.txt,s,$nick) != $null) {
    write -ds $+ $nick awaynames.txt
  }
}
on *:text:*:#:{
  tokenize 32 $strip($1-)
  if ($regex($1,/^!?\b(brb|amsg)\b/i)) {
    if ($regml(1) = brb) {
      var %check = $read(awaynames.txt, s, $nick)
      if ($null != %check) notice $nick You're already recorded as being away.
      elseif ($2- = $null) {
        write awaynames.txt $nick - None.
        notice $nick You have been marked as away.
      }
      else {  
        write awaynames.txt $nick - $2-
        notice $nick You have been marked as away.
      }
    }
    else {
      var %check = $read(awaynames.txt,s,$$2)
      if ($$2 ison $chan) {
        if ($null != %check) notice $nick  $+ $$2 $+  $+ : %check
        else notice $nick  $+ $$2 isn't recorded as being away
      }
      else notice $nick That person is not in this room.
    }
  }
  else {
    var %check = $read(awaynames.txt,s,$nick)
    if ($null < %check) {   
      msg #  $+ $nick $+  is back from: %check
      write -ds $nick awaynames.txt
    }
  }
}