Scanned articles are kept on the web server for 21 days.
If more than 21 days has passed since you received your notification email you may re-request the article using the online ILL.
If you accidentally deleted the article within 21 days of being notified simply reply to the notification email or email the Interlibrary Loan Office which filled your request with as much information about the request as you have and we will try to re-post the article for you.
We advise that you save your articles as soon as you receive notification, just to be on the safe side.
Have more questions? See the LibGuide: http://guides.library.upenn.edu/resourcesharing