As an H-1B holder, you are permitted to work for your H-1B sponsoring employer in your H-1B status. You will lose H-1B status once you use EAD to work for your current or any other employer and you would be in I-485 pending status. If your I-485 application is denied, you are no longer authorized to stay in the United States as an H-1B holder and will have to leave the country.