What happens if my NIV has expired while my employment-based green card process is still going on?
Filing the I-140 petition does not confer any status upon you, so filing this alone will not allow you stay in the US without having NIV status. Once you file the I-485, which you can do as soon as your priority date is current (possibly at the same time you file your I-140), you will be in a temporary status known as Adjustment of Status (AOS). This allows you to stay in the US until you receive an adjudication on your I-485, even if your NIV has expired. AOS does not give you work authorization, but you are allowed to file an I-765 for an EAD card with your I-485, which gives you authorization to work anywhere in the same or similar career field that was the basis for your I-140. Keep in mind that it typically takes 1-3 months for the EAD to be approved. If you plan on traveling between the time your NIV expires and your I-485 is approved, you can file an I-131 to get an Advance Parole (AP) document that allows you to travel while your I-485 is pending. This AP also takes roughly 1-3 months to receive.