Hi @FabianHoll ...
I may be completely wrong on this, but my gut feeling on this is that any content that a user shared to Canvas Commons (be it a full course or a single item such as a page, assignment, discussion, etc.) would remain in Commons for others to potentially import into their own course(s). However, to be absolutely sure, I suggest that you reach out to Canvas Support to see what they have to say. You can contact the Canvas Help Desk staff by using the following link:
How do I get help with Canvas as an instructor?
Please come back to this topic to provide an update once you have had a conversation with Canvas Support. Thank you!