Generally speaking, original routing credit only applies for day of departure changes, such as IROPS or taking a bump. You usually can't get ORC for a change that happened months in advance. That said, the OP should be OK, as even though CZ isn't a SkyTeam member, you can still earn DL miles flying them as long as they ticketed you in an eligible fare class. Check the partners page for details:
https://www.delta.com/content/www/en...-partners.html
I don't know the rules about baggage.
Also, since DL changed the carrier you're flying, you can refund the ticket for no charge and buy a new one if you prefer.