hi @impulskiel welcome to the forum 
- user deletion doesn’t affect locally stored data… it just blocks access to the server…
- during login desktop client generates a device password and remains logged in even after a password change. for this reason a wipe command should success once the client connects to the server next time.
https://docs.nextcloud.com/server/latest/developer_manual/client_apis/RemoteWipe/index.html
But I would recommend you test the procedure as some reported wipe didn’t work as expected… Remote wipe doesn’t work as expected