I would assume that blocking Apple would mean both removing iPhone app and blocking iPhones from all Google sites.
In fact, if Apple were stripping out Google ads (as per some rumblings), Google would have a basis to demand that all it's affiliates stop serving to iPhones as well.
War would be hell at that point. Probably some lawsuits in the making.
Then maybe Apple can find another Youtube and Google Maps provider. Question is: will the branding stuck in our minds supersede what Apple's route to alternatives entail? All theoretical, nonetheless.