To maintain your green card during extended absences:

• Brief trips under 6 months are generally fine. 
• For longer absences Apply for a re-entry permit, allowing travel for up to 2 years.Consider filing  Form N-470 to preserve continuous residence for naturalization.
• Avoid absences of 6 months or more; return within 6 months each time.
• Maintain strong ties to the U.S. (family, home, job) to demonstrate intent to reside permanently.
• If travels are work-related and you have significant U.S. ties, your green card status is less likely to be at risk.
• Absences of one year or more can lead to loss of green card status without proper documentation.

If your employer fails to pay you after starting your H-1B employment, it can pose challenges for future H-1B transfers. To address this:

• File a complaint with the U.S. Department of Labor's Wage and Hour Division.
• You can file online or by phone (search for "LCA complaint US Department of Labor").
• This complaint serves as evidence explaining the lack of pay stubs during future H-1B transfers.
• Employers must start paying when you're ready to work or within 30 days (if coming from outside the US) or 60 days (if already in the US), whichever is earlier.
• Filing a complaint may help you recover unpaid wages and protect your ability to transfer your H-1B in the future.

The ability to keep your NIW when changing employers depends on whether you continue to pursue the same endeavor that was the basis for your NIW approval. If you maintain the same type of work in the same field, even with a different employer, you likely can keep your NIW. However, if you change to a completely different field or type of work, you may need to start a new green card process. For certainty, it's advisable to consider filing a new green card application or NIW when changing employers.

The USCIS is currently focusing on two main aspects when evaluating NIW petitions:

1. National Importance of Your Work:

They want to see how your specific work benefits the entire country, not just your immediate sphere of influence.

Example: For a neurosurgeon, saving lives locally isn't enough; they want to see a broader national impact.

2. Comparative Contribution:

USCIS is looking at how your work stands out from others in your field.

They want to see that your contribution is not just significant but also distinguishable from your peers' work.

These two factors are currently the primary focus in NIW evaluations, leading to higher rejection rates for petitions that don't adequately address these specific points.