No offense to your code, Slade, however, in my opinion, running a timer every 10 seconds would be a waste of resources.

Checking the number of users upon joining, is a good idea, but once that's done, then one only needs to check after people part, quit or are kicked.

In regards to the usage of $cid, for a code like this, it's not necessary, as the checking doesn't have to be done over multiple networks.
Here's my current recommendation for a full code
Code:
on me:*:join:#:{
  chkusers $chan
}
on !*:part:#:{
  chkusers $chan
}
on !*:quit:{
  chkusers $chan
}
on *:kick:#:{
  if $knick != $me {
    chkusers $chan
  }
}
alias chkusers {
  if $nick($1,0) == 1 {
    part $1
  }
}