For now..

Code:
on *:join:#: .timercheckchan $+ $cid $+ # -o 0 5 checkchan $cid #
alias checkchan {
  scid $1
  if (!$window($2)) {
    .signal close $1-2
    .timercheckchan $+ $1 $+ $2 off
  }
}


Then you can use:

Code:
on *:signal:close: echo -s Window $2 on CID $1 just closed.