Hey there -
You are submitting to SharePoint Library? When you set up your submit connection, you have the option to overwrite existing. If you ensure your file name for the submit will be unique, you can safely do this - take the whole saving thing off the table - users can just submit, and their updates update the existing item.
You have to make sure you set the file name to be something that won't end up set again - so, thinking back on the other thread you and I were talking in, if you are using some logic to set your file name field, you'd only want to run it if the field were blank, you don't want to be accidentally creating dupes....