There are two approaches here.
Firstly, attrition, simply don't replace those that leave. Given the sheer size of the company, a hiring freeze and attrition would gradually reduce the size of the workforce. I'd be astonished if a company with a market cap of $1.2 trillion would be likely to collapse if it didn't immediately get rid of 12,000 people right now.
Second, stop over recruiting in the first place.
I'm sure google, like the others this week have some company mantra about how precious their staff are, and they're all family. Until they're not.