You need a Visa to enter a country and you have to maintain/have valid status to stay in the country. If your h1b gets approved, you will get a new I-94 card with initial validity maximum of 3 years and duration of status is changed to teh validity of your new I-94 card. Having said that you don't need to have h1b visa to remain here,but once you leave US you need to have a visa stamped in your passport to get in unless you are PR or a citizen or a citizen of a country whose visa gets automatic revalidation. As far as getting your H1B visa stamping is concerned,its always better to write those consulate information in your h1B application as it expediates the process of sending approval confirmation to the consulate section where youmight be appearing in the future to get your h1b visa stamping done. so the bottom line is you don't need to leave US when your h1b gets approved. Hope-it helps a little.