Companies don't have the infrastructure in place to track former employees and see what they are doing just for the purpose of filling law suits. So unless they create a Unicorn and become famous, they are pretty safe no matter what.

I once heard a VC Pitch from a bunch of patent trolls who wanted to create a company that you could subscribe to called "IP Insurance", that would then track your former employees and sue them when they violated their contracts automatically. With the added bonus that they would somehow buy the litigation contract from the original company so negative PR would be all on the Insurance company.