It's a decision you need to weigh up for yourself. On the other hand, it might continue to work for many years. If it stops working because of changes in operating systems or Adobe finally turns off the activation servers, you're stuck. The perpetual licence allows you to use the software indefinitely for a single payment, but I wouldn't describe it as being a 'lifetime licence', except in the sense of the lifetime of the software. When Adobe moved to the subscription system, it said it would make CS6 available for the foreseeable future, but that no updates would be made, unless a major security risk were discovered. If you want to buy it, you can find a Buy CS6 link at the top left of the following page: Dreamweaver Help | Help and tutorials. The current version of Dreamweaver (CC 2014.1) is version 15, so CS6 is already considerably out of date, and not officially supported by Adobe. The only version that's still available with a perpetual licence is Dreamweaver CS6 (version 12), which was released three years ago. UPDATE: Adobe stopped selliing Creative Suite in 2017, 3 years after this thread began. You cannot buy Dreamweaver CC on a perpetual licence.
