If a mild smell is still there once fermentation finishes, time and racking off the lees clear a lot of it on their own. Beyond that some brewers briefly expose the mead to clean sanitised copper, tubing or a copper scrubber, which reacts with sulphur compounds.
Read properly on that before trying it rather than taking a forum comment as a method. And to answer the real question: no, this is not a ruined batch. Plenty of meads that stank during fermentation come out fine once the cause is dealt with and they have had time.