Hi Jeff
We have what is called Durable Unsubscribe where if a lead is re-created and has previously unsubscribed then the new lead will be unsubscribed.
They must then opt-in to re-subscribe.
Please see the following Article: https://community.marketo.com/MarketoResource?id=kA650000000GxXxCAK
Just to note and agree with Josh, just beauce they unsubscribe is not the only item you should look when deciding to remove a lead. There is alot of valuable information in the dehavioral data. Also a Lead may re-subscribe via the actions listed in the above article.
Thanks
Damien