This is a good question--currently, content on our servers is kept indefinitely.
In terms of archiving/deleting content, we leave that up to our clients (i.e. you in this case). 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, to archive/delete content, you'll need to archive/delete Snaps individually.