Whitmer not in the running for VP, but very much in the team! She's the Harris campaign co-chair! (I'm looking now to find who the other co- is) #politics
Co-chair doesn't mean there are just two; the Biden campaign had seven co-chairs as well as a campaign chairwoman, campaign manager (the senior position), and other functions.
Probably several of the co-chairs will continue into the Harris campaign and maybe a few new ones will be appointed.