Will my iMessages be saved if I log out of my Apple ID?
Hello! if my iMessages aren’t saved in my iCloud and I log out of my Apple ID when they be gone if I log back in?
This may help: https://support.apple.com/en-us/HT208242
I infer, from the document, that messages will remain. I've never logged out of all devices and I use iCloud messages.
Found this too: Both iMessage and FaceTime will still be functional when you sign out Apple ID on your iPhone. However, these services will only work if you have a phone number connected to your FaceTime and iMessage. If you used your Apple ID for your iMessage or FaceTime, you will not be able to send iMessage texts or make FaceTime call.