Zoro still has unresolved plotlines this arc:
No, Zoro is NOT "Done" After Defeating King
No he has not. Oda only said that Ushimaru is not his father. Zoro being the second coming of Ryuma was highlighted at the start of his fight with King:
Here's a thread on Zoro's connection to Oden:
A look at Inherited Will in the Land of Wano
No it was not. Cutting a magma dragon that no one saw is meaningless and has nothing to do with Zoro's Ryuma plotline:
The Second Advent
You're wrong.
Should Kaido die, the most likely person to kill him is Zoro:
Here's a thread:
Long Live ZKK