And gmail has 1 Billion monthly active users, so that is quite likely a conservative guestimate.
I don't think its implausible that shutting down these guys accounts will cost google a 7 or 8 figure sum in (non budgeted) backbone bandwidth charges alone.
And you don't pay per megabyte at the peered networks scale, or even 95% percentile.
Just a significant number deciding it is time to back up their content.
And at the backbone level it is all charged by the Mbps for example http://www.level3.com/en/legal/ip-traffic-exchange-policy/ http://blog.streamingmedia.com/2014/02/transit-works-costs-i... So a jump in a significant portion of the user base from a few MB per user per day to several GB will be several thousand times more expensive for that day.
Putting traffic into a tier 1 network costs, taking it pays.
A massive surge from Googles hardware onto the tier 1 networks will be very, very expensive.
Last time it came up was as the BitTorrent protocol started blowing up ISPs that couldn't pay the bills.