Even if they weren't in business though, there'd still be an issue with trying to do anything with DECtalk while not having a license, because the software's never been open sourced and the license has never been changed to be more permissive. And those kinds of copyright fights where the company has shut down but someone still owns the rights get real wild real fast.
Companies do this all the time. Especially when their websites aren't the primary drivers of their business. I mean they shouldn't, and they should at least keep the domain, but it happens.