How secure is to join startup for H1B? What happens when company gets aquired?

Hi, I am on H1B in US. I have offer from startup that have 6 employees. I want to know how secure it will be considering I am on work visa.I want to have GreenCard processed. Can someone please comment what happens to green card processing when startup gets aquired ? I usually takes 6-7 years for green card to get approved ( in EB2 category). Any advice ? Appreciate your input.