Not going to argue with you either way but I think you're forgetting the orange section in your scenario. How many of the original 20k will support, and only support the Bobcats? It's a tough question and nigh impossible to answer but I don't think it's safe to assume they'd all stay in the newly doubled 40k.
I'm sure the blue section is larger anyway so it's probably moot, but just didn't want you to miss a fairly important aspect.
10,000 loyal to Bobcats (orange)
15,000 loyalto Hornets (blue)
20,000 combined (purple)