The biggest threat to Big Tech is regulation, but these companies are so deep-pocketed they could regulatory capture and lobby their way out of anything. There could be minor setbacks for the unicorns who haven't been doing so well in public markets, but this isn't a 2000-esque situation that would impact all companies: just the late arrivals who existed at the right place at the right time, when way too much capital was chasing far too few opportunities (the Lyfts/Ubers/AirBNBs/etc).
You seem to assume that the current tech investment bubble will gently deflate with minimal collateral damage. But judging by the historical record, it's far more likely to go out with a bang along with a general market overcorrection, the least of which is a whole bunch of startup software engineers suddenly looking for a job. Google had almost nothing to do with the GFC, but it still froze hiring for a while in 2008 when Lehman Brothers collapsed.
The salaries will be there so long as the profit and margin is there to pay them, versus the relative scarcity of labor supply. It's that simple.
Microsoft, for one example, will double in size in the next ten years and they're already generating ~$50 billion per year in operating income (next four quarters).
They're going to fire people while doubling in size, from their already extreme scale? Nope.
Adobe is now worth as much as SAP. They're booming, extracting vast profit from their global cloud business. They'll more than double in size in the next ten years, their operating income will zoom from $3b to $6b or more. They're going to fire people in that environment? Nope.
The same is true of Google, Facebook, Amazon, Apple.
Apple will fire people while generating $60-$70 billion per year in operating income? Nope.
So where will the labor slack come from in tech to reset salaries lower? It's not going to.
Plus, the Fed has its hands all over the financial system in several ways that it didn't in 2007. Rates will stay perma low by necessity, they'll drown everyone in inflation before they allow rates to ever rise beyond 3% again for a consequential duration of time (it'll bankrupt the US Government, they can't allow it for the same reason Japan couldn't). Those perma low rates will provide a very large support base under valuations and will persistently push money to chase greater risk (public multiple expansion; and VC capital flowing very freely).
When there is inevitably a large downturn or correction, the low rates and massive QE injections will make the bottom higher than it otherwise would be. The next downturn will be far more gentle than the great recession (and the bounce back to prime conditions also might be even slower).
The only way any of this changes substantially, is if US tech is decimated by foreign competition. US tech can pay so well because they dominate globally, extracting vast global profit and paying a relatively small number of employees (vs the profit scale) from that big haul. That's the equation that has to change to drain US tech salaries.
That money does not come from thin air. If the rest of the economy implodes or even stalls, it means less companies buying ads and less people buying new shiny iDevices, which will impact FAANG as well.
As for foreign tech eating American tech's lunch, it's pretty clear that the next big social network will be (already is) TikTok, which is Chinese.
Google had nothing to do with 2008 indeed, but look at where tech salaries are today. Clearly that unrelated disaster was not going to impede tech's climb. I considered the parent poster's question within the context of uniquely big tech risks. Global economic risks impact all industries; there's nothing particularly unique there. If we have another global crisis, we could tank for a bit, then recover, and FANG staff salaries could end up exceeding the $500-600k mark. When implying these "golden years" could end, do we mean a local maximum or an absolute maximum? We could be quantifying this a bit more precisely to uncover more insightful reasoning.
