For the end user, there's no difference between "Google still has my data but I can't access it" and "Google lost my data". Especially with Google's customer service being about as effective as a wishing well
Right but this doesn't necessarily have to be a drive failure. (Pun not intended.) Imagine if there was some id collision due to a db migration or something, and then one user ends up deleting the other user's data accross all backups. Unless google never deletes any data, even when the user deletes it themselves, then you can't be saved from that.
Theoretically possible, but (super super super) unlikely. I'd also think that when a user "permanently" deletes their data, it would still be on Google servers for a specified time (maybe a week?).
Again, all guesses. But if someone offered me a bet, I'd wager 1:10,000 that the data is permanently deleted. Extremely unlikely.
There are many types of backups (e.g. replication, point-in-time replication, periodic incremental backups, periodic full backups) and not all of them project against the worst kind of issues, e.g. a software bug that accidentally deletes a whole bunch of data.
The risk is that the bug impacts a small number of users and they decide not to bother with a restore just to recover data that only impacts 0.001% of users.
Or they don't notice at all because the support forums have no way to get in touch with engineers.