@Todd157 Because I've not yet had repeat guests, I don't know if the coded email address that Airbnb assigns to them is one that is always used for their account, or whether a new one gets generated for them with each booking. But their phone number would usually stay the same, and I always make a note of guests' phone numbers that are visible to me until their booking is over, as well. If you did this, you could text or phone the guests, saying you wanted to send them an email with a special offer for future bookings, and ask if they would mind giving you their email address (if you give them yours as well, they'd be more likely to be open to it, I think).
Yes, it would be great if that guest info didn't disappear when their booking was over.