The following prompt should be added:
"You are saving this file as part of a draft email. Any changes to this file may be lost if you don't save a copy to your computer. Would you like to save a copy to your computer?"
Currently, if I open a draft that has an attachment, edit the attachment, then click save, the file saves as part of the draft, but does not save to the original location on my computer. I am not prompted that the file location is not on my computer. So, if I delete the email, or if I remove the attachment, all edits are lost.