Also, there's degrees of exit. Google can exit the market and have zero presence in the EU whilst still sub-licensing tech to affiliates who pay for the privilege and resell their stuff, whilst dealing with all the local regulatory overheads. Plenty of firms use that sort of model.
its psychology, the board or ceo would react preemptively based on the idea that shareholders would react on their behalf
shareholders (if they have voting power at all) would react for the same result at higher fine amounts than that
1. Other search engines regularly appearing in news / on screens would remind the non-EU users about alternatives.
2. Lost traffic is lost information. Google still relies on knowing your behaviour to improve targeting.
3. Giving a whole region to other search engines would build up their financial standing and they could threaten Google in other regions in the future.
The fine would have to be in range of 100 billion for them to exit
And this is setting aside the costs of compliance to avoid more fines. Even if the costs are less than another fine, they're not nothing. You're looking at an entire year's profits from the EU essentially being wiped out by this fine, plus reduced profits going forward due to increased compliance costs and probably losing sales. And this is your best case scenario.
It would not take a 100 billion dollar fine to make Google leave the EU, it would only take another fine like this one.