You could re-create the deleted record in marketo by making use of an Apex callout (you could use Push Lead endpoint) from SFDC to the Marketo (but you should be careful while using it as they will cost you your marketo API requests). Also for this you need to prevent the creation of lead in marketo upon form fill-outs and instead update the record first in sfdc and then make apex callout so the existing lead record gets synced in the marketo with all the fields as is. I am not sure if this is the most efficient and fail-safe approach or not. We have a setup in our instance where-in we do not create the multiple records in marketo for the same lead showing multiple product interest but create seperate records in SFDC (so different products' sales rep can followup on separate records in crm) for each product interest of the same lead.
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