I have been having the same problem running Mountain Lion 10.8.2 with iPhone 4 running 5.1.1. I have not updated to 6 because I have heard too many complaints. Nonetheless, I get the same popup, and if I "sync now" I would have lost over 600 photosas Google would have erased them from Contacts.app.
Here is what I did to potentially solve the problem, while still maintaining an Apple-Google Sync in the future...
First, I made sure the my apple contacts were fully up to date, and synced with facebook. Basically, I wanted my macbook contacts to be as "up to date" as possible, so i went through several iterations of ensuring that facebook, twitter, and my current contacts.app were all in sync. While I was doing all of this, I kept pressing "sync later" on the google popup that is in question if it ever appeared.
Then, I synced with my iphone running 5.1.1 to ensure that my iphone had the most recent contacts from my mac, and vice versa. I double checked on the macbook that there were no duplicate contacts, and merged anything that was duplicated. I also refreshed the connection to facebook and twitter contacts by going into system preferences > mail accounts > update contacts for both facebook and twitter.
FINALLY. I went into contacts and into preferences and unchecked the box for "sync with google" ... see the attached image.
Then I repeated the same process of ensuring that contacts.app, and facebook, and twitter were all in sync.
THEN I went back to the check box (As shown in the attached picture, and re-enabled the google sync. My hope is that the fresh connection to Google would let the Google Servers know that all of these contact on the macbook are actually the most current version (And thus, to leave them the **** alone!).
So far, so good. I did get a popup asking me which versions of my contacts were correct. But this pop up let me choose either the iphone, the contacts.app, or google. It didn't force me to delete any photos.
I'll post again if it fails. If you don't here back from me, assume it's still working.