I believe you are referring to Telerik Platform Analytics Data Retention (as indicated in the Analytics "Data Retention" plan) where data older that the supported history window (which at the moment for Telerik Platform Business License is 6 months) will be deleted. This applies only to accumulated Analytics data.
The above is not applicable to Telerik Platform Backend service data - Application backend data, Users, Push Notifications, Files, Business Logic, etc. The backend services data will be preserved as long as you have an active Telerik Platform account, so there is no retention window and backend services data for your applications will not be deleted after 6 months.
Upon suspension or termination of the active Telerik Platform account (as per the current Backend Services License Agreement. point 2.7), Telerik guarantees to hold Applications and their content (Data, Users, Push Notifications, Files, Business Logic, etc.) for a period of 30 days, after which the account's data may be deleted.
Let me know if this has answered your question.