In the Mail app, tap and hold on the photo until you see this:
Select "Save Image" to store it in Photos - Camera Roll.
What you're describing with the email account, seems to be deleting it from your iPad. There is no option to close an account in Settings - Mail, Contacts, Calendars.
To force close an app, double tap the Home button to reveal the multitask bar, then slide the picture above the app icon towards the top of the screen.