It's not that difficult to create a bot / script that undoes edits made from a list of IP's / IP ranges.

What's needed, basically, is to:
* check RecentChanges for edits by the targeted IP's
* use EditCopy to quickly revert the edit
* 'touch' the page using a different IP to purge the EditCopy

In PseudoCode rather than real code (lest any one tries and uses such a contraption against this site):
 Every couple of minutes:
 {
   Fetch RecentChanges from the server
   For each IP on list:
   { 
     filter for IP address
     For each mentioned page not removed:
     {
        Send http request for EditCopy
        Send http request to click Save button
        From different IP address:
        {
           Send http request for Edit
           Add or delete one whitespace character (null changes are rejected)
           Send http request to click Save button
        }
      }
    }
 }
The above is easily done in PerlLanguage, JavaScript or similar. A bit harder, but certainly doable, in C++ or similar.

More complex versions could possibly:
* Detect earlier changes by an IP and revert to a version ''before'' that
* Instead of reverting to before that version, merge those changes out, leaving other people's contributions intact
* Detect spam cleanups and leave those alone, even if done by the targeted IP

Detecting ''any'' edit by user JohnDoe coming from any random IP and deleting those while leaving a consistent version of the page is very possibly AiComplete, and could only be done by a human masquerading as a bot.

But what even the simplest version of such a bot would do, effectively, would be denying edits by a particular user or group of users, since most of us have either a fixed IP or an IP within a certain range.

MichaelSparks seems to have used a similar approach in fighting spam (since a lot of spam seems to come from a limited range of IP's).
----
See also: WikiBot, WikiVandals, DefensiveScriptIdea