> H1B's are immigrant visas
No, H-1B visas are explicitly nonimmigrant visas for temporary workers. [1]
> They terminate in greencards after one renewal
No, they don't. You can apply for a GC, but there's nothing automatic about the process, and the GC is not guaranteed to be approved either.
[1] https://www.uscis.gov/working-united-states/temporary-worker...