Don't give up just yet trying to contact the author. Ping the author again via email. Search other modules the author wrote to see if there's a more current email address. Try a web search for the author as well. Give yourself maybe another week after your best efforts at tracking down him/her.

If you still haven't heard anything by then, send mail to modules@perl.org, or post to comp.lang.perl.modules, asking whether anyone is still claiming to maintain the module in question. If no one in those forums can vouch for someone currently owning and maintaining the module (after another reasonable wait, another week or two), then you can probably feel free to take over and upload a new version to CPAN yourself.

If you do, don't take this ownership lightly. If you're really going to take over, be prepared to field questions, fix bugs, etc., in the future. If you're not interested in doing that, but really just want to make your one fix available, then at least document the fact that the ownership is up for grabs, so the next person in your situation isn't left wondering like you are now...

(Eric Raymond covered this property/ownership aspect of open source software in his Homesteading the Noosphere, essay, which will be part of his eventual The Cathedral and the Bazaar book.)