A) Assuming you keep copies of all folders/emails locally B) Assuming Google isn't evil and won't delete all your mail first before shutting down your account, thus causing your IMAP client to sync their deletion
B) I’m not sure Google ain’t evil. Even if they’re good, if I fail security on my side, some other evil person, unrelated to google, may be able to delete all my e-mails before shutting down my gmail account. That’s why e-mail client alone is good but not enough, also need backups of that local DB.
We can't know that. There is no recourse when they do screw people and it would look the same from the outside whether it was an automated system or a manual one (or more likely, a mix of both).
B)That's why you do backups. (In the same vein as RAID is not a backup, IMAP by itself isn't one too).
An easy way to do that is to have an IMAP client on another machine that you sync manually.