Benutzer gestorben - was ist zu tun?

How very sad. My commiserations.

I am not sure that OSM has a fully described procedure. In a couple of cases where I have known the deceased contributor this has been handled by close family members or friends. I can put you in touch with some of these people if you contact me off this forum (see my OSM Wiki page).

I think the key things are:

• Inform someone in the sysadmin team.
• If you have access to Wiki & OSM accounts, add a short notice advising people not to try & contact the user.
• Post notices to relevant mailing lists &/or forum, but only if an active contributor.
• Possibly create a automated reply for messages emanating from OSM-based systems to handle the likely case that people don't read profiles.
• If possible, change email accounts for the wiki & OSM.

Sysadmins may desire more additional information: it is not unknown for online identities to be compromised through people claiming third-parties have died.