If you delete a teacher's profile in Sdui , all groups in which that person was the sole group admin will automatically be set to "One-Way Communication".
In these groups, the remaining group members will no longer be able to use the group chat.
You can find out more about this in the article:What does “one-way communication” mean? ‍

This is a security mechanism so that, among other things, students in a class or course group cannot write to each other unsupervised.

Existing individual chats with the teacher's deleted profile will continue to exist so that no information is lost.

Note: Since the profile no longer exists, the respective chat will be renamed "Unknown Conversation".