When you opened the email attachment, you were provided the opportunity to open the attachment or to save it to disk. You describe that you chose to open it.
You modified the contents of the "file".
When you closed it, PPoint asked to save it. Perhaps you did choose to save it.
When you closed the email, you were advised that the contents had changed, and asked if you wanted to save them. If you said No, the changes were lost to the embedded copy. If you said Yes, the changes were saved, in the embedded copy.
If you said No to the final save question, your best bet is to search your temp folders for *.ppt.
I cannot locate a test copy. So, look at the email attachment to see if your changes are there. If yes, file save as to a known location, like desktop or documents.