Here is some info from the article announcing the changes: https://nation.marketo.com/docs/DOC-3836-changes-to-marketo-salesforce-sync-under-the-hood#jive_content_id_Cleaning_Up_S…
"Uninstalling the MLM package deletes fields, data and workflows created by the package. Any dependencies like for reports or workflows inside of SFDC that you have created based off of these fields will need to be removed manually. If these other custom dependencies exist, they’ll need to be removed before uninstalling the MLM package."
No, there is none. anyway, if some of the fields in MLM are still being used, the uninstall utility will raise some errors and stop. You will have to remove all the references to these fields before you can complete the removal of the package.