I use dokuwiki as a personal site, and don't really let anybody else modify my pages. Instead of telling a user they have followed a link which doesn't exist, which shouldn't ever happen, could dokuwiki display a 404? This way I can also monitor server logs for pages that don't exist, and supply the users browser with what they expect when a page isn't there.
I had a quick look at the code but headers had already been sent by the time dokuwiki checks for the existence of the file, which makes it a little difficult to hack in for my version only.
A configurable parameter that lets the user choose between "normal wiki" and "404" would be very useful for me, and I imagine maybe other people too.