Something

on *:START:{ set %minUsers 5 } 
on 1:INVITE:#:{ 
join $chan 
timer $+ $chan 1 10 /ckUsers $chan 
} 
alias ckUsers { 
if ($chan == harpbot) {HALT}
  if $nick($1,0) < %minUsers { part $1 a minimum of %minUsers users are needed for the bot to stay. } 
}