Storing documents locally or in cloud services from within Teams
Dear respected,
As per the description, I understand that there have the Teams chat retention policy in your tenant, but you want to know if the files will be deleted along with the messages after 7 days. Please correct me if I made any misunderstanding to your scenario.
When files are shared in Teams channels, they are indeed auto-saved into the Documents folder in the team's SharePoint drive. However, the retention policy for Teams chats and messages does not directly affect the files stored in SharePoint.
Retention policies for Teams chats and messages dictate how long messages are stored in a chat or channel, but files shared via these messages may have their own separate retention policies. This means that even if the messages are deleted after 7 days, the files in the SharePoint Documents folder will not be deleted unless there is a specific retention policy set for those files in SharePoint.
Reference: Microsoft Teams messages about retention policies - Microsoft Support
You can have a quick confirmation with this by easily accessing the file storage location from Teams channel>switch to the Files tab>click Open in SharePoint button. Below I have attached a screenshot from my tests for you just now, hope it can provide a better reference.
From there, in the SharePoint document library, you can check if there have all previously files stored, if yes, then I believe the tenant has setup no specific retention policies set for SharePoint Documents folder. If not, there may have specific retention policies that govern the retention and deletion of the files.
Please correct me if I made any misunderstanding or if there have anything else I can do for you.
Your patience is highly appreciated. Hope you a nice day and stay safe!
Best Regards,
Mia