What is the difference between deleting and removing a participant from a group conversation?

It is not the same when you delete participants or you remove them from a group conversation.

Deleted participants can no longer access the conversation and the conversation is no longer listed in their conversation list. They can neither view the conversation history even up to the time they were deleted. On the other hand, when you remove participants from a conversation or a Conference Bridge, they can still view the conversation in their conversation list and the conversation history up until the point that they were removed.

In both cases, you can leave a conversation or delete yourself from it, unless you are the only person from your domain participating in the conversation. Deleted or removed participants can rejoin the conversation, if they are added back by another participant. Once added back, they can view the entire conversation history including all updates that happened between the point they where removed or deleted and the point they rejoined.