Markets can remain irrational longer than you can remain solvent - John Maynard Keynes
If you work for a big tech company, try to partner with the startups doing interesting work in your domain. When they run out of money you can scoop up their IP (and maybe team?) for cheap.
Can you short sell a company that doesn't have a public offering?
Yes but you would have to make that deal with the private investor(s).