Something

on *:join:#:{
  if ($chan == #Peer) || ($chan == #Splodge) || ($chan == #Sky-Fatality) || ($chan == #omgwtfhax) halt
  if ($nick == $me) {
    usercheck
    if (%users. [ $+ [ $chan ] ] < 5) {
      timerpart 1 5 /part $chan Channel does not meet minimum user levels (5 or more users)
      unset %users. [ $+ [ $chan ] ]
      else halt
    }
  }
}
on *:part:#:{
  if ($chan == #Peer) || ($chan == #Splodge) || ($chan == #Sky-Fatality) || ($chan == #omgwtfhax) halt
  if ($nick != $me) {
    usercheck
    if (%users. [ $+ [ $chan ] ] < 5) {
      timerpart 1 5 /part $chan Channel does not meet minimum user levels (5 or more users)
      unset %users. [ $+ [ $chan ] ]
      else halt
    }
  }
}
alias usercheck {
  set %users. [ $+ [ $chan ] ] $nick($chan,0)
}