If it troubles you, use backup account settings from time to time.
Recovering account settings then becomes a little (or a lot) easier.
Clearly, saving the backup remotely is better than leaving it on the device, but as the backups have passwords too, you can protect them if they stay on the device. Advantage is only one password for any number of accounts. I use "generated" 16 character passwords on my several email accounts, so only using backup or writing them down could possibly work!
Only one to remember, then, but of course only one to forget....
On the subject of passwords, I just had my tablet replaced due to a fault, and it was a bit of a head scratch to transfer the backup file between devices, without having the email already working, and without an on the go USB connector to use a USB drive. In the end I had to upload into Dropbox, but you cannot download from Dropbox to aqua mail backup folder, so I had to download it first to the downloads folder and restore the email on the new device from there. I note that some apps allow access to Dropbox, but aqua mail not.
Done now, but:
Is there an easier way?