You'll remain on the Pro plan until the time you have already paid for expires. After that you will be returned to the Free plan. Your private presentations will remain private.
If the account is on Trial your team will deactivate immediately. If you have already been billed, your team will remain active until the end of your current billing period.
User accounts associated with a team are not accessible once the team has deactivated. They are not downgraded to free since they may depend on content – such as themes – which is only available within the team.