You can create a new lead for contacts by assigning to a SFDC queue. Contacts can't be owned by queues so Marketo would create a duplicate record on the lead object. Its not recomended but can be done.
You should think about creating a custom field for Contact Status and map Lead Status values to this. This way you can see leads and contacts through the funnel.
Also, impliment a new inquiry task process in SFDC and add your lead status pick list values in here. Build this task process into your Marketo flows. When an existing lead/contact shows renewed interest a task is generated for your lead/contact owner. Train sales to handel Tasks as new leads with SLAs.
Some options for you.