Assuming gmail and g-suite share technology, I doubt any enterprise customers would be comfortable with the content of the email actually being purged. I'd guess there is some backdoor for corporate compliance and auditing reasons. I also don't see any reason you couldn't build a bot that grabs these for you to keep via the gmail add on api.
wait. why wouldn't at least some corporate customers be interested in this sort of thing? they'd have a standard, non-selective, purely time-based expiration policy which would be defensible in the face of a government investigation. "Your honor, we made no attempt to hide specific details about this matter. Our policy has always been to destroy all messages that are greater than 90 days old."
Others would not because the regulators (like the SEC) have said that companies can't delete communication data (email/chat) prior to regulated windows. most companies want to delete as soon as possible after that window has expired which is it's own challenge.
I suppose I wanted to point out that not being able to read a message and fully purging it are not the same thing and gsuite likely alienates the enterprise if they cannot comply with regulation.