I didn't know about this:
.de domain names, like some other ccTLDs do not have expiry dates. They live on as long as long you pay for them. That's why German providers often charge for the domain names by the month (around €1 or less/month is typical).
So basically there's no way for you to know when the domain expires as it's still being paid monthly. Contact Denic.de indeed, seems like all domain name registrations are centralized there but my guess is they'll tell you there's nothing they can do if the domain it's still being paid regularly.
I'll try to contact the relatives in that case.
Okay, interesting, thanks for looking this up!
If the domain is still getting paid for, I have no problem. Since we are pretty sure no one is paying for it anymore. If so, that would be really mysterious.
Hopefully they will reply soon. I used info@denic.de now and I got at least an automatic reply now.
As the former owner of a webhosting company, you'd be surprised at how often this kind of thing happens. There are sites that live on for years after people have died, it's kind of wild how long some things will keep auto-renewing on billing for, even to a dead guy's credit card.