[moultano]

The behavior in this case is that new uploads are blocked but your existing files remain.

https://support.google.com/drive/answer/2736362?hl=en "If you cancel your storage plan or when your storage plan expires, your storage limits will reset to the free levels for each product at the end of your billing cycle. Everything in Google Drive, Google Photos, and Gmail will still be accessible, but you won't be able to create or add anything new over the free storage limit. If you reach or exceed the free storage limit"

[nkkollaw]

Ah, that would make me a lot more confident.

Don't a lot of people archive terabytes of stuff and just leave after 1 month, though?

[mavendependency]

Gmail would refuse to recieve mail until you either free up space or upgrade. They share the same storage space.