Well I didn't have anything like that coded, but I just cooked this up. I have no idea if it works or not since I couldn't find a netsplit to test it on (for a change) so buyer beware.
Code:
on *:quit:{
  if (*.* *.* iswm $1-) {
    ; Quit was a result of a netsplit
    if (!$hget(netsplit)) hmake netsplit 10
    elseif (!$hfind(netsplit, $replace($1-,$chr(32),@), 0, w)) timer 1 5 netsplit_show $1-
    ; If hash table 'netsplit' doesn't exist, create it
    ; Else if there are no entries in 'netsplit' for a split between servers $1 & $2 (first detection of this netsplit) then start timer
    var %i = 1, %item
    while $comchan($nick, %i) {
      %item = $replace($1- $ifmatch,$chr(32),@)
      if ($hget(netsplit,%item) == $null) echo -c info $comchan($nick, %i) * Netsplit occurring between $+(,$1,) and $+(,$2,...)
      ; If no item already exists with the name %item (the first detection of this netsplit in this channel) then echo to that channel
      hadd netsplit %item $addtok(%item,$nick,32)
      ; Add this nick to the list of nicks split from this channel
      inc %i
    }
  }
}
alias netsplit_show {
  var %i = 1
  while $hfind(netsplit, $+($replace($1-,$chr(32),@),@*), %i, w) {
    echo -c info $gettok($ifmatch,-1,64) * Following nicks lost in netsplit: $&
      $replace($hget(netsplit,$ifmatch), $chr(32),$+($chr(44),$chr(32)))
    ; For each entry in 'netsplit' matching for the split between servers $1 and $2 echo the list of nicks that have split
    inc %i
  }
  hdel -w netsplit $+($replace($1-,$chr(32),@),@*)
  ; Delete all trace of this netsplit
}