Good question!
(And to potential close-voters: The fact that Apple will provide their own mapping is public)
I'd suggest you file a radar with Apple, and duplicate it on http://www.openradar.me/
As to your questions:
Can google be kind enough tolerate old apps can still be used in this context?
They could, and I believe in practice they probably will be.
Is google preparing their own Mapkit API we could use on iPhone could it be available on previous IOS releases so developers could update their apps before IOS6 is released?
Very probably. But I doubt it'll be ready in time for you to update your app before iOS 6 release.
Can Apple provide an option to still display Google Map to bridge the gap until their provide similar Web services?
I don't think so. I don't think they'd want to, and I think their licensing contract with Google will expire in the not-too-distant future.
