If a lead is synced to Dynamics and then that is converted to an opportunity, should that contact return and create another lead shouldnt the standard connector create another lead.
It seems to be appending the lead to the opportunity. Is that the correct standard connectors behaviour?
If the lead is converted to opportunity, that lead now is a contact record in CRM and Marketo (MS Type = Contact). Down the road, if that person becomes a "lead" once again, you will not be able to sync that record to CRM again (since the connector does not allow you to sync that record as a lead to CRM when it already exists as a Contact in CRM). Which is why we use this purposeful duplicates approach that is documented here: Create multiple leads per Marketo person record