We use the change owner feature within Marketo to help keep our contact & account owners set to the same person. We have it where there is never a time when these do not match. When I run the change owner flow within Marketo, I get all SFDC users that have ever existed. I would love to have it updated so that it will only pull currently active SFDC users. There's no reason to assign an owner to someone that is not active in SFDC. In Salesforce, if you try to assign something to an inactive user, it won't let you so I don't see why Marketo would.