I was referring to (mostly) internal projects in "German Mittelstand". Some of them with external partners. Customers might have the same problem, though, if they rely on the expertise of a single specialist. Regular customer support is usually available 8 hours per day, 5 days per week, but that's not what I was referring to. They usually don't manage projects.
What are you talking about? I was referring to German companies where we don't have proper holiday replacements for internal projects, as well as for those with external partners.
If it is a small company, then the owner will answer. If it is bigger, holidays will be planned so that no interruption will occur.
Companies can close completely for a week, usually between Christmas and New Year. That's all.