Nothing you can do. This is the implicit (and sometimes explicit) contract we have with cloud services, that they’ll keep our data safe and keep the lights on forever. If you think about it, though, unless you’re paying for it this is untenable. A single user, when paying with their attention, will only ever generate a fairly fixed amount monthly. And yet the cost of keeping them on as a user grows steadily over time as more data is accumulated.

You pop3 your mails or keep a local copy of you imap them. That’ll make sure you don’t lose any historical communication.

As soon as you start doubting if the service with persist, start switching services over to a new address, logins first.

I would recommend getting a Google Takeout export every year or so. Even before it falls off a cliff it’s a good idea to have your own backups. Accounts can get blocked, hacked, etc.