AOL Mail does not have an auto-save function for composing email, but depending on the software you are using on your Mac, the draft email may be placed in a Mail Waiting to Be Sent folder. This is likely the case if you are using installed software from AOL. If you are just using AOL Webmail in a browser like Safari or Firefox, there is no Mail Waiting to Be Sent folder.
Either way, if the email is still up on your screen, you should be able to send once the connection is restored. If the email is not on your screen and is not in a Mail Waiting to Be Sent folder, then you will likely need to recreate the message.