Conversation transcripts are stored in an archive for a 13-month rolling window. They are available on demand for review during this period. On the other hand, metadata of the conversation is stored within the Dynamics 365 CRM.
If needed, you can also have "Transcript Storage" enabled on your account. This will cause the conversation transcripts to be duplicated inside your Dynamics 365 CRM. The transcripts would then persist past the 13-month window. If you would like this to be enabled on your account, please contact our support team.