If you exit a group, you'll be removed from the group. However, you'll still see the group in your Chats tab and be able to read the chat history. If you're the only group admin and you exit a group, a participant is chosen at random to become the new admin.
To exit a group:
After you exit a group, you have the option to delete the group. When you delete the group, you'll no longer see the group in your Chats tab and the chat history will be erased. To delete a group after exiting a group: