H1B and I-140 validity?


My PERM application was approved in Dec 2020 and my I-140 was filed with a premium procession on Jan 22nd, 2021. I have the following questions,

  1. Since my I-140 was filed with a premium processing I am expecting approval by Feb 22nd, 2021, is my estimation correct?
  2. If I were to leave the US after completing 180 days (ie. after Oct 23rd, 2021), can my employer still revoke my approved I-140?
  3. My H1B is valid till Nov 2023; do I need to have a US visa and stay in the US to keep my approved I-140 valid and in-queue for GC?