If you leave a team, that team will be removed from your conversation list. If the team is public, you can rejoin that team at any time. However, if the team is private, you will need to receive an invite from an existing team member in order to rejoin that team.
It’s also important to note that when you leave that team, that team does not lose the conversation history that you’ve contributed, even if you were the original creator of that team.
Also note that if you’re the only admin of that team, you will be unable to leave that team until you assign another member as an admin.