If the person who has been removed, they won't find out that they have been removed from the group unless they open the chat and check. They will continue to see the old chat, names of the participants, export the contacts and also export chat as pdf but will be unable to send or receive any further messages.

What happens if you are removed from a WhatsApp group?

When you delete a group, you'll no longer see the group in your chats list and the chat history will be erased from your phone. Other participants will still see the group in their chats list. However, no one will be able to send messages.

How can I join a WhatsApp group after removed?

If you want to rejoin a group chat you left, the group admin will need to re-invite you to the group. If you were the only group admin and left the group, another participant was chosen at random to become the new admin. You can ask the admin to re-invite you to the group and make you a group admin again.