This script returns the percentage and names of inactive users. It does this by doing a '/whois' and then using the data.

The instructions are inside the code.

;+-------------------------------------------------------------------------------------+
;| Inactivity Report (for mIRC 6.35+) - by vSkyzv                                      |
;| ------------------------------------------------------------------------------------|
;| Usage Instructions:                                                                 |
;| 1. Right click on the "Nicklist" (the list of names on the right)                   |
;| 2. Goto "Control"                                                                   |
;| 3. Click on "Inactivity Report"                                                     |
;| 4. Wait two seconds for the script to start sending "/whois" commands               |
;| 5*. Wait for the data to finish (it may take a long time in large channels).        |
;| * If you want to stop the script before it finishes, close the dialog.              |
;| ------------------------------------------------------------------------------------|
;| Troubleshooting:                                                                    |
;| * If errors are found, please type "/unset %active.*" without the quotes.           |
;+-------------------------------------------------------------------------------------+

menu Nicklist {
  .Control
  ..$iif(%active.trigger,$style(2)) Inactivity Report {
    inc %active.trigger
    set %active.chan $chan
    dialog -m inactivity_report inactivity_report
    names $chan
  }
}
raw 307:*:{ if (%active.trigger) { haltdef } }
raw 310:*:{ if (%active.trigger) { haltdef } }
raw 312:*:{ if (%active.trigger) { haltdef } }
raw 313:*:{ if (%active.trigger) { haltdef } }
raw 319:*:{ if (%active.trigger) { haltdef } }
raw 320:*:{ if (%active.trigger) { haltdef } }
raw 355:*:{ if (%active.trigger) { haltdef } }
raw 361:*:{ if (%active.trigger) { haltdef } }
raw 366:*:{ if (%active.trigger) { haltdef } }
raw 378:*:{ if (%active.trigger) { haltdef } }
raw 311:*:{ if (%active.trigger) { haltdef | inc %active.whoised } }
raw 317:*:{
  if (%active.trigger) {
    haltdef
    if ($3 > 600) { set %active.inactive.list %active.inactive.list $2 ( $+ $round($calc($3 / 60),2) minutes) }
    else { set %active.active.list %active.active.list $2 ( $+ $round($calc($3 / 60),2) minutes) }
  }
}
raw 318:*:{
  if (%active.trigger) { 
    haltdef
    if (%active.whoised == %active.nicks) {
      var %active.inactive.count = $calc($numtok(%active.inactive.list,32) / 3 / %active.nicks * 100)
      var %active.active.count = $calc($numtok(%active.active.list,32) / 3 / %active.nicks * 100)
      did -i inactivity_report 4 1 Inactive Users ( $+ %active.inactive.count $+ % $+ ): $iif(%active.inactive.list != $null,%active.inactive.list,No users are inactive)
      did -i inactivity_report 4 2 Active Users ( $+ %active.active.count $+ % $+ ): $iif(%active.active.list != $null,%active.active.list,No users are active)
      did -i inactivity_report 4 3 Other*: $calc(100 - (%active.inactive.count + %active.active.count)) $+ %
      did -i inactivity_report 4 4 *Users that fall into the "Other" category are users who do not submit idle information such as network services.
    }
  }
}
raw 353:*:{
  if (%active.trigger) {
    haltdef
    set %active.nicks $calc($numtok($1-,32) - 3)
    set %active.loop %active.nicks
    var %delay = 0
    while (%active.loop > 0) {
      inc %delay
      timer 1 $calc(%delay * 2) whois $gettok($remove($4-,:,~,&,@,%,+),%active.loop,32)
      timer 1 $calc(%delay * 2) did -o inactivity_report 2 1 $round($calc(%delay / %active.nicks * 100),0) $+ %
      dec %active.loop
    }
  }
}
dialog inactivity_report {
  title "Inactivity Report" 
  size -1 -1 300 167
  text "Gathering Data:",1,10 10 80 15
  edit "0%",2,95 7 40 20
  text "Statistics:",3,10 40 80 15
  edit "Edit2",4,10 55 280 80, multi hsbar vsbar
  button "Copy Statistics to Window",5,10 140 280 22
}
on *:DIALOG:inactivity_report:*:*:{
  if ($devent == init) {
    did -d $dname 4 1
    did -b $dname 2
    did -m $dname 4
  }
  elseif ($devent == sclick) && ($did == 5) {
    var %active.inactive.count = $calc($numtok(%active.inactive.list,32) / 3 / %active.nicks * 100)
    var %active.active.count = $calc($numtok(%active.active.list,32) / 3 / %active.nicks * 100)
    echo 5 -a Inactive Users ( $+ %active.inactive.count $+ % $+ ): $iif(%active.inactive.list != $null,%active.inactive.list,No users are inactive)
    echo 5 -a Active Users ( $+ %active.active.count $+ % $+ ): $iif(%active.active.list != $null,%active.active.list,No users are active)
    echo 5 -a Other*: $calc(100 - (%active.inactive.count + %active.active.count)) $+ %
    echo 5 -a *Users that fall into the "Other" category are users who do not submit idle information such as network services.
  }
  elseif ($devent == close) { unset %active.* }
}