Will Records in Salesforce Re-sync into our Marketo if we delete their records from Marketo?

[sshamo]

 We are looking to delete records in our Marketo database to clean it up. We currently have our Marketo synced to Salesforce.

Questions:

1. If I use a smart campaign to delete records in Marketo but choose to keep them in our CRM (Salesforce), will these records re-sync over to Marketo after we delete them? Or would the only thing that would introduce them back into our Marketo database be activity on our resources from them after they are deleted?
2. If I need to create criteria in Salesforce for these leads to not be re-synced over, how should I go about doing so?
3. If we were to delete someone from our Marketo but they remain in our SFDC, what would cause them to resync with Marketo? Would it be activity in Marketo? Edits on their Salesforce record? Would it sync back automatically immediately after the initial deletion?

[JessicaMeyers]

Do you currently have a "one to one" sync between Marketo and Salesforce? If yes: 

1. Yes the records will re-sync from Salesforce during the next sync cycle.

2. If you need them not to sync you need what is called a "sync filter" essentially it is a field in salesforce that says "yes send this record to Marketo (or no don't send this record to Marketo). there are MANY posts on this. Here is a good one.

If you already have a sync filter in place. 
1. Before you delete from Marketo be sure to update whatever your sync filter field is to ensure they don't sync back! 

As I said above, there is a lot in the community on sync filters, they are a popular topic, but they don't come without some things to be aware of!