It will be a business decision of Google. They could want to use it now as an incentive for people to switch to android phones. They're also not going to get licensing fees from Apple for the Map data anymore so it may not make sense from a revenue perspective to create an app.
I would think it would be in their best interest to hold off for a bit till more people find out what they are now missing and demand grows. If one is submitted, Apple could delay indefinitely putting it on the phone to avoid the embarrassing prospect of people switching back en mass to Google maps.
Personally I am holding off upgrading to iOS 6 because I like Google maps more.