When these tech giants have layoffs - usually in the 100s or 1000s - it's a big hit to the job market. May not be reflected on Craigslist or Dice, but there'll be a lot more job-seekers. Instead of getting 50 resumes per job posting, hiring managers would be getting hundreds.
"To big too fail" isn't a thing.
Bottom line is - hiring (or lack of) is a leading indicator of a company's financial health. A company that doesn't have any open jobs for a sustained length of time (3-6 months to a year) is in belt tightening mode - which comes right before layoffs or worse, closing shop.
Btw - Yahoo is already doing layoffs or 'downsizing'. If Yahoo wasn't hiring during the past 3-6 months, that definitely was an indicator of this.
Yahoo Downsizes In Latin America, Closes Mexico And Argentina Operations http://techcrunch.com/2016/01/28/yahoo-downsizes-in-latin-am...
Here are some news sites that track layoffs. I recommend keeping a close eye on things.
http://techcrunch.com/tag/layoffs/
https://twitter.com/search?q=layoff%20OR%20layoffs%20OR%20%2...
Or better yet, keep an eye on the Dice jobs number which is prominently displayed on the Dice.com home page.
As of today, January 29, 2016 that number is 84,201. My take is that if this number goes below 60,000 then the bubble is bursting.
The latter has such massive hiring needs in comparison that even if funding dried up (which they do not need since they have lots of profit and are already oftentimes publicly traded), I don't think it would slow down the market THAT much.