As its name suggests, deleting a user/data source is irreversible. However, revoking access for a user or a data source will disconnect access but will help reactivate those users or data sources should you need to reconnect.
It is a very friendly feature if you have multiple data sources and/or users in your account since you can activate the connection or user by revoking them if you want to reconnect.
Keep that in mind that neither delete nor revoke is counted as an active data source, so it won't be counted as an active source in your current plan.
Questions about revoking/deleting users or data sources? Contact [email protected].