Currently, content on our servers is kept indefinitely.
In terms of archiving/deleting content, we leave that up to our clients. Generally, our users will implement their own policies here--some keep the content indefinitely, while others may clear everything after a certain time frame e.g. 3 months.
In terms of execution here, to archive content, you'll need to delete Snaps individually. This can be painstaking, I know. We are looking forward to introducing a feature to make this easier at some point, although it won't be in the short term (likely over 3 months away).